22.06.2026

Calculating Floor Area: Definition, Structure, and Examples

Building design

View from below of a multi-story residential building – architectural photography by michaelseh

Anyone who wants to develop a property, file a building permit application, or appraise a building cannot avoid one key figure: the floor area. Calculating floor area is not a bureaucratic formality, but rather the foundation of every decision regarding planning law, economics, and structural engineering in building construction. It determines how much usable space a plot of land can accommodate, what a building is worth, and how building rights are translated into square meters.

What gross floor area is and how it differs from related area terms
Which standards and regulations define the calculation and what differences exist between them
How the floor area ratio (FAR) works and what it means in terms of planning law
Which areas are included in the calculation and which are not
How the calculation is performed step by step using concrete examples
What role attics, basements, garages, and ancillary facilities play
What common errors occur during the calculation and how to avoid them
How floor area is used in the context of zoning plans, building permit applications, and property appraisals

What Is Floor Area? Definition and Scope

Floor area refers to the sum of the floor areas of all full stories of a building, measured based on the exterior dimensions of the building’s walls. It is one of the key parameters in German planning law and is used in the Building Land Use Ordinance (BauNVO) as the basis for calculating the floor area ratio (GFZ). Anyone wishing to calculate floor area must first understand that this term should not be equated with other area measurements in construction, even if they overlap in meaning.

The most important distinction is between floor area and usable floor area and living area. Usable floor area, as defined by DIN 277, describes the area within a building that is actually usable, broken down by type of use, and accounts for wall thicknesses, columns, and fixtures as deductions. Living area, as defined by the Living Area Ordinance (WoFlV), is defined even more narrowly: It applies exclusively to residential buildings, excludes stairwells, basements, and certain ancillary rooms, and applies deductions for sloped ceilings. Floor area, on the other hand, is measured from the exterior and serves as a control parameter in planning law, not as a description of actual usability. In practice, this distinction is often a source of misunderstandings.

Closely related, but not identical, is the floor area of a single story. The floor area of a building is calculated by adding the floor areas of all full stories. A three-story building with a floor area of two hundred square meters per story therefore has a total floor area of six hundred square meters. It sounds simple, and in principle, it is. The pitfalls lie in the details: What counts as a full story? What is included in the calculation, and what is not? And which set of regulations should be followed?

Legal Basis: BauNVO, State Building Codes, and DIN 277

In Germany, floor area is primarily regulated by the Land Use Ordinance (BauNVO), which, as federal law, forms the basis for zoning plans. Section 20 of the BauNVO defines floor area and specifies how it is to be calculated. According to this provision, floor area must be determined based on the exterior dimensions of the building across all full stories. What constitutes a full story is determined by the respective state building codes, as the definition of a full story is a matter for the individual states. This is where one of the key complexities in calculating floor area begins: those building in Bavaria work with different definitions of a full story than those planning in Hamburg or North Rhine-Westphalia.

State building codes generally define full stories based on the clear room height and the proportion of the exterior wall area that reaches a minimum height. In most federal states, a story is considered a full story if its ceiling height reaches a certain minimum height—often 2.30 meters—over at least two-thirds of the floor area. Attic floors that do not meet this condition do not count as full stories and are therefore not included in the floor area calculation under the BauNVO. The same applies to basement floors that do not meet the criteria for a full story. This regulation has significant implications for the usability of properties and is a frequent subject of disputes under building law.

In parallel with the calculation under planning law, there is DIN 277, the standard for floor areas and volumes in construction. It serves other purposes: cost estimation, space management, and building valuation. DIN 277 does not define “floor area” as used in the BauNVO, but instead uses “gross floor area” (GFA) as an umbrella term. The BGF encompasses all floor areas of all floor levels of a building, including structural areas, and is therefore generally larger than the floor area under planning law. Anyone wishing to calculate the floor area must therefore always clarify which set of regulations they are following, as the results can differ significantly from one another.

The Floor Area Ratio (FAR): Planning Control via Ratios

The floor area ratio, abbreviated as FAR, is the ratio of a building’s total floor area to the area of the lot on which it stands. It is the most important tool used by zoning plans to control the building density of an area. A GFZ of 1.0 means that the sum of all full-story floor areas is equal to the lot area. A GFZ of 2.0 allows for twice the floor area relative to the lot area, which can be achieved, for example, by having four full stories with a floor area ratio of 0.5.

The formula is: Floor Area Ratio equals floor area divided by lot area. Conversely, the maximum permissible floor area is calculated by multiplying the Floor Area Ratio by the lot area. A lot of five hundred square meters with a specified FAR of 1.2 thus allows for a maximum floor area of six hundred square meters. How this area is distributed across the stories—whether across two stories of three hundred square meters each or four stories of one hundred fifty square meters each—is a matter of the building’s shape and other specifications in the zoning plan, such as eave height or the number of stories.

Section 20(4) of the Federal Building Code (BauNVO) permits certain areas to be excluded from the calculation of floor area. These include areas of common-use rooms on floors other than full stories, provided that these floors are not considered full stories due to their use and nature, as well as areas for garages and parking spaces. These exceptions are significant in planning law because they provide flexibility in land use. At the same time, they are a source of errors if planners apply the exceptions incorrectly or are unfamiliar with the definitions of full stories in the respective federal state.

Calculating Floor Area: Step by Step with Examples

The calculation of floor area follows a clear pattern. First, all full stories of the building are identified. Then, for each full story, the floor area is determined based on the exterior dimensions of the building walls. Finally, these floor areas are added together. It sounds simple, but in practice it requires a careful examination of each individual case.

Here’s a first example: A detached single-family home with a ground floor and an upper floor, both with exterior dimensions of ten by twelve meters, results in a floor area of two times one hundred twenty square meters, or two hundred forty square meters. The attic has been converted but does not meet the criteria for a full story under the applicable state building code because the clear ceiling height is below the minimum height over more than one-third of the floor area. It is therefore not included in the calculation. The basement is located entirely below natural ground level and is also not considered a full story. The floor area for planning purposes is therefore two hundred forty square meters.

A second example shows an urban apartment building on a lot measuring three hundred square meters. The building has four full stories, each with external dimensions of eight by fifteen meters, or one hundred twenty square meters each. The floor area is four hundred eighty square meters. The floor area ratio (FAR) is calculated as four hundred eighty divided by three hundred, or 1.6. If the FAR specified in the zoning plan is 1.5, the project in its current form would not be eligible for approval. The planner would have to either reduce the number of stories or decrease the floor area per story.

A third example addresses a special case: a stepped story that is considered a full story under the State Building Code because its exterior walls reach the minimum height over more than two-thirds of the floor area. The floor area of this stepped story is sixty square meters because it is set back from the stories below it. These sixty square meters are fully included in the floor area calculation, even though the story is smaller than the others. In practice, stepped stories are a frequent source of confusion because their classification as full stories depends on the specific design and the State Building Code.

Special Cases: Attics, Basements, Garages, and Auxiliary Facilities

Attics are the most common special case when calculating floor area. Whether a converted attic is considered a full story depends on the ceiling height above the floor area. Many state building codes require that the clear height be at least 2.30 meters over at least half or two-thirds of the floor area. If this threshold is narrowly missed, the attic does not count as a full story and is excluded from the floor area ratio (FAR) calculation. This circumstance is deliberately exploited in the design phase: An attic that remains just below the full-story threshold offers additional usable space without affecting the floor area ratio (FAR). Whether this strategy works in a specific case must be coordinated with the relevant building authority.

Basements are considered full stories if they extend above the natural ground level and meet the criteria for a full story. A semi-basement that protrudes halfway above ground level and has sufficient ceiling height may be classified as a full story, depending on state building codes. Fully underground basements, on the other hand, generally do not count as full stories and are not included in the floor area ratio calculation. For building owners, this means that a deep basement can provide significant usable space without affecting the floor area ratio (FAR), provided it does not exceed the full-story threshold.

According to Section 20(4) of the Federal Building Code (BauNVO), garages and parking spaces are not included in the calculation of floor area, provided they are used exclusively for parking and garages. This exception applies to underground garages as well as to garages located on full stories, provided they are used exclusively for parking vehicles. However, if garage spaces are used for other purposes or are part of a mixed-use concept, the exception may not apply. Ancillary structures such as tool sheds, bicycle storage rooms, or trash sheds that do not constitute full stories are also excluded, provided they do not meet the definition of a full story.

Common Mistakes When Calculating Floor Area and How to Avoid Them

The most common mistake when calculating floor area is using interior dimensions instead of exterior dimensions. The BauNVO explicitly stipulates that floor area must be determined based on the exterior dimensions of the building walls. Anyone who bases their calculations on floor plans with interior dimensions systematically underestimates the floor area by the thickness of the wall structures. For solid exterior walls with a thickness of thirty to forty centimeters and insulated structures, this error can amount to several square meters per floor, depending on the building’s size, which adds up to a significant deviation when there are multiple floors.

A second common error is the incorrect assessment of whether attic and basement floors qualify as full stories. Planners who are unfamiliar with a state building code or who do not know the current version risk incorrectly classifying floors as full stories or vice versa. Since the definitions of full stories vary between federal states and are occasionally amended, it is essential to review the currently valid version of the state building code. In case of doubt, it is advisable to consult with the responsible building authority at an early stage.

A third error involves confusing floor area with gross floor area. Anyone who is supposed to calculate the floor area according to the BauNVO for a building permit application but instead determines the gross floor area (BGF) according to DIN 277 will provide a figure that, while formally correct, is unsuitable for planning law purposes. Both values may be similar, but they are conceptually different. GFA includes all floor levels—including basements, utility rooms, and levels not considered full stories—while floor area under the BauNVO covers only full stories. In practice, this confusion regularly leads to additional requirements from building authorities and delays the approval process.

Floor Area in Context: Zoning Plan, Building Permit Application, and Property Valuation

In the zoning plan, the floor area ratio (FAR) is one of the most important specifications alongside the plot area ratio (PAR), the type of construction, and building lines. It determines how intensively a plot of land may be developed and is thus an urban planning tool that controls density, mixed-use development, and the cityscape. Downtown neighborhoods dating from the Gründerzeit era often have floor area ratios (FAR) ranging from 2.0 to 3.0, while single-family residential areas are often limited to floor area ratios (FAR) ranging from 0.4 to 0.8. These figures are not arbitrary; rather, they reflect urban planning principles and infrastructure capacities.

In the building permit application process, the calculation of floor area is an integral part of the application documents. Most state building codes require a floor area calculation as part of the application package, demonstrating that the planned project does not exceed the specified floor area ratio (FAR). This calculation must be transparent, accurate, and based on the building’s exterior dimensions. Incorrect or incomplete floor area calculations are a common reason for inquiries or rejections during the approval process. For architects and planners, a solid command of floor area calculation is therefore an essential part of their toolkit.

Floor area also plays a role in property valuation and real estate law. The income approach and the cost approach, which are used in real estate valuation in accordance with the Real Estate Valuation Ordinance (ImmoWertV), rely on area-based metrics related to floor area. The floor area ratio (FAR) is also a key indicator when assessing building land reserves and infill potential: If the actual FAR is significantly below the value permitted under planning law, there is theoretically potential for infill development. Whether this potential can actually be realized depends on additional zoning regulations, the development status, and the actual building dimensions.

Floor Area as the Basis for Precise Planning

Calculating floor area is far more than just a mathematical exercise for the building permit application. It is the point at which abstract planning law is translated into concrete square meters, where urban planning goals meet the individual property, and where architects, planners, and developers jointly explore the limits and possibilities of a project. Those who have a firm grasp of this calculation understand not only the numbers but also the planning decisions behind them.

The differences between floor area, gross floor area, usable floor area, and living area are not mere academic quibbles. They have tangible consequences for permits, costs, and usability. Those who clearly distinguish between these terms and are familiar with the applicable legal framework can avoid costly mistakes and lay the groundwork for robust planning. This applies equally to new construction on greenfield sites, infill development within existing neighborhoods, and the renovation of a historic townhouse.

Ultimately, the calculation of floor area serves as a prime example of how building law and construction practice intertwine. The Federal Building Code (BauNVO) sets the framework; state building codes fill it with concrete definitions; and planners translate both into drawings and calculations. Anyone who understands this triad—who knows why an attic floor sometimes counts and sometimes doesn’t, why garages are excluded from the calculation, and why exterior dimensions apply—possesses a tool that is indispensable in every phase of the planning process.

22.04.2025

Architecture

44 residential units in Saint-Denis from DREAM

Building design

The new building with 44 residential units by DREAM. Photo: Cyrille Weiner

Two decades after the devastating fire in a dilapidated residential building on Rue Fraizier in Saint-Denis, a new construction project marks a turning point in the urban development of the north of Paris. The Parisian agency DREAM (Dimitri Roussel) has realized a residential ensemble with 44 units there – half for rent, half as subsidized ownership according to the “Bail Réel Solidaire” (BRS) model. It is the first project of its kind in Saint-Denis. However, the ambitious gesture is less about architectural showmanship and more about functional, mass-produced housing that strives for social integration.

The new building stands on a site that has been derelict since the fire in 2001. The fire at the time drastically exposed the dilapidated conditions in the old building, which was being used by shark tenants. The ensuing vacancy was perceived not only as a physical defect, but also as a social one. DREAM now sees the project as a contribution to “repairing” the neighborhood – and to re-establishing trust in the urban space.

The 44 residential units are spread across several buildings and follow a clear principle: as much individuality as possible within the standardized production. Almost all of the apartments are open-plan, with many facing in several directions. The majority have generous outdoor spaces – balconies or gardens at ground level. Interior qualities have also been considered: separate entrance areas with storage space, daylight kitchens that can be closed off if required and large window openings with panoramic views are all part of the repertoire.

The floor plan design is based on the charter of Plaine Commune, the inter-municipal association responsible for the area. The urban positioning of the buildings responds to morphological and climatic analyses of the site. A typical planning response is, for example, the staggering and orientation of the volumes to optimize daylight and natural ventilation.

In terms of design, DREAM dispenses with design experiments. Instead, the architectural expression arises from the materiality and rhythm of the façade. Wooden slats, metal panels and open balcony structures made from a combination of wood and metal structure the outer shell. Great importance was attached to prefabrication: The timber frame construction walls, including cladding, windows and shading elements, were manufactured entirely in the factory. The self-supporting balconies also arrived on site pre-assembled.

This strategy has several advantages: Firstly, it increases the quality of execution, and secondly, it reduces the construction time – a factor that plays a particular role in the densely built-up and socially sensitive Saint-Denis. All in all, the result is a residential building that relies on CO₂-reduced construction methods without playing this off visually.

What is striking about the project is the effort to establish communal zones alongside the private living space – a concept that is often referred to elsewhere as “third places”. In Saint-Denis, the elements are simple but effective: a large, inviting entrance area, green inner courtyards with passageways and roof gardens that serve as places to retreat and meet. The lobbies act as semi-public buffer zones between the street and the apartments. Visual references to the courtyard are intended to provide not only light but also social control.

The whole project was designed in collaboration with the public housing association Plaine Commune Habitat. The aim is to appeal to a heterogeneous group of residents – both people on low incomes and young families who want to build up property through the BRS model.

With a construction cost of around seven million euros and a living space of 2,775 square meters (SHAB), the project is within the scope of what is feasible in a subsidized context. The “NF Habitat” certification and compliance with the French thermal insulation regulation RT 2012 with a 20 percent reduction underline the ecological focus.

Those involved in the project include Bollinger+Grohmann (structural engineering), ENEOR (building services), Le Sommer (certification) and Topager for the landscape architecture. Cap-Exe was responsible for coordinating the various trades.

What can be deduced from the project in Saint-Denis for the current housing debate? Certainly not a new type. Rather, it shows how a combination of solid planning, serial production and municipal control can make a contribution to sustainable urban development – beyond creative exaggeration, but also without falling into banal functionality.

The architecture remains restrained but deliberate. It unfolds its effect through everyday use – as a place to live, to meet and to reappropriate a long-neglected urban space.

31.10.2024

Ukraine war: Мы за мир

Building design

As a result of the war in Ukraine, the European architecture scene has quickly taken a public stand against the Russian war of aggression. G+L also stands in solidarity with the Ukrainian people and government.

BIG, David Chipperfield Architects, Foster + Partners, gmp, Herzog und de Meuron, MVRDV, OMA, Snøhetta, Zaha Hadid Architects – as a result of the war in Ukraine, which violates international law, the who’s who of the European architecture scene publicly opposed the Russian war of aggression in a very short space of time at the end of February/beginning of March 2022. Within just a few days, numerous offices expressed their solidarity with the people in Ukraine and with all those who stand for peaceful coexistence – above all via social media. In the case of Chipperfield, HdM, OMA and Zaha Hadid, the public statements were followed by an immediate halt to all construction projects in Russia. BIG also announced in a statement that the office would not be carrying out any projects in Russia or for the Russian government. However, it is not clear from this whether a construction freeze has been imposed or whether there are simply no Russian projects currently in progress.

First the governments, then the private sector. Today, our globalized world also makes it possible for corporations, companies or even planning offices to impose sanctions. So while Apple, Siemens, Starbucks, McDonalds, Coca-Cola, Pepsi and the management consultancies KPMG, PWC, EY and Deloitte are suspending their business in Russia as a result of the war of aggression, or Elon Musk is actively supporting Ukraine with the help of his satellite internet service Starlink, including reception systems, the world of architecture is also drawing its own conclusions. This is worth a special look, as it was or is precisely non-democratic regimes such as Russia or China that have provided the big star offices with unique construction projects in recent years. The M+ Hong Kong designed by HdM only opened at the end of 2021. While at the turn of the year in Moscow, the Renzo Piano Building Workshop RPBW converted the GES-2 power station into a center for visual and performing arts for the V-A-C Art Foundation.

Jacques Herzog on democratic architecture

For us in the editorial team, this immediately (and once again) triggers the question of how political planning can be, but also how political planning must be. What is exciting in this context is that Jacques Herzog in particular has repeatedly publicly addressed the question of democratic architecture. You can think what you like of him and the HdM projects, but he takes a stand. As he did in an interview in 2020 with Lukas Gruntz from architekturbasel.ch. Referring to the historic urban development of St. Petersburg, Venice, Rome and Paris, he said here: “Perhaps more beauty is created in a non-democratic context because the context is more extreme, more radical.” But he also continued: “From our point of view, an enlightened and democratic society, architecture must be anchored in the population and ideally emerge from the needs of the population.” Sentences that should make us think. Now more than ever.

Ukraine war: Coop Himmelb(l)au under pressure over Crimea project

Lighthouse projects in non-democratic regimes must be better considered in future. I wonder what is going through Wolf D. Prix’s head at Coop Himmelb(l)au right now? His office was criticized even before the war of aggression. Since 2020, the Viennese have been planning two of the four cultural buildings that Vladimir Putin wants to be built by 2023. The particularly tricky case is the planned opera house on the Crimean peninsula, which was annexed by Russian occupiers in 2014 in violation of international law(more on this in an SZ-Plus article). With reference to the lighthouse project, Ukrainian President Volodymyr Zelensky imposed economic sanctions against the Viennese architecture firm and six of its representatives on January 21, 2022.

Wolf D. Prix: Coop Himmelb(l)au is building an opera house, not barracks

According to an SZ.de article by Gerhard Matzig, who interviewed Prix on the subject, this was preceded a year and a half ago by threats from the Ukrainian embassy to Coop Himmelb(l)au. Prix would not be allowed to build the opera house in Sevastopol or the architectural firm would soon be ruined. And according to Gerhard Matzig in his article, Prix has now also been advised to distance himself from the project and Putin. When asked by Matzig whether he would do so, Wolf D. Prix sighed on the phone. Prix is of the opinion that he is not building a barracks, but an opera house. As a cultural project, this is not subject to the embargo regulations. Unsurprisingly, as of mid-March 2022, Coop Himmelb(l)au still has no statement on the Ukraine war.

Ukraine war: Russian planners make their mark

But now back to those who openly oppose the war. Because it’s not just the European star offices that are flying the flag. According to SZ.de, a total of 6,500 Russian architects, designers and urban planners also signed an open letter on the website of the Russian architecture magazine “Project Russia” between February 26 and March 4, 2022, calling for an immediate end to the war. The tragedy is that this appeal also fell victim to the “fake news” law against critical reporting on the Russian army signed by Vladimir Putin on March 4, 2022. Only a short version of the campaign with a picture of a dove of peace can now be seen on the site. It says here in Russian: “Unfortunately, we were forced to remove the text of the letter under threat of criminal liability under the law that came into force today. We are for peace!”

One profession, one passion

Meanwhile, however, the Union of Architects of Ukraine also called on the International Union of Architects to expel the Union of Architects of Russia from the organization. “Those who do not condemn Russia’s actions support them,” the Süddeutsche Zeitung quotes the President of the National Union of Architects of Ukraine, Oleksandr Chyzhevsky, as saying in a letter to the UIA. If you let this statement sink in, you have to ask yourself – even if you condemn Russia’s actions in the strongest possible terms – whether we really want to live in a world in which people from one industry, one profession, one passion, go against each other simply because of their nationality. For this very reason, the G+L editorial team would like to join our Russian colleagues: Мы за мир. We are for peace. And we condemn the Russian government’s attack on Ukraine, which violates international law, and stand in solidarity with the Ukrainian people and government.

Ukraine war: bdla and BAK also active

While German landscape architecture firms are still quite reluctant to express their solidarity, the bdla published an official solidarity statement #StandWithUkraine on March 2, 2022. The bdla declared its “deepest regret about the war in Ukraine, the loss of human lives.” It condemns this attack, which violates international law. The bdla’s thoughts are particularly with its colleagues from its partner association, the Guild of Landscape Architects of Ukraine. In the same letter, the bdla refers to the initiative of the Federal Chamber of Architects. This has set itself the goal of becoming active beyond expressions of solidarity. For this reason, the BAK is making its network available to the Ukrainian Association of Architects. The goal: sleeping places for refugees. Find out more here.