Calculate Buildable Floor Area
Updated:
With AZ, GFZ, BMZ, ÜZ, or GZ and your parcel's area, calculate instantly how much floor area, volume, or footprint is allowed — and how much reserve remains after subtracting an existing building — for the GZ, how much green space is required at a minimum.
This calculator uses only the values you enter and is not tax, legal, construction, or financial advice. For an actual building project, consult the communal building authority or a qualified professional.
Calculator
Select your commune's index, enter its value and the parcel area — the result appears instantly, right in your browser. Enter the index value as a decimal (0.3, not 30 %); both the index value and the parcel area are your commune's countable values (the countable / anrechenbare floor area and plot area from the BNO).
- 1.Pick the index your commune uses: AZ, GFZ, BMZ, ÜZ, or GZ.
- 2.Read the index value off the PLR cadastre (the land-use planning theme) or your commune's building and zoning regulations.
- 3.Enter the parcel area in square metres — optionally also an existing floor area, volume, or footprint.
- 4.The calculator shows the allowed floor area or volume (for the GZ, the minimum green space required) and the remaining reserve or the gap to the minimum instantly, right in your browser.
Enter the index value and parcel area to see the result.
A negative reserve does not automatically mean a violation — a density transfer, an older permit, or a different measurement method can explain the difference. For a binding assessment, the communal building authority is responsible.
This result is based solely on the values you enter above. alpflo makes no claim about any specific parcel — to find the index value that applies to your commune, check the PLR cadastre or the communal building and zoning regulations (BNO).
Why you can work out buildability yourself
The formula behind every index is simple arithmetic: index value times parcel area. You only need to know which index applies in your commune and what its value is — both are in the PLR cadastre or the commune's own building and zoning regulations.
AZ and GFZ — the floor area ratio and floor space index
Regime: the floor space index (GFZ) is an IVHB term (Annex 1 no. 8.2): the sum of all floor areas over the countable parcel area. The floor area ratio (AZ) is not an IVHB term; it comes from cantonal law. The arithmetic is the same either way: allowed floor area = index value × parcel area. Which areas count as floor area is set by the law that applies. Aargau, Obwalden, Schaffhausen, Uri and Zug joined the IVHB but kept the AZ by reservation; Zurich did not adopt the GFZ and stays with the AZ. In cantons that have not joined, the cantonal building act applies.
Source: IVHB Annex 1, no. 8 (lexfind.ch) · Glossary: floor area ratio · Guide: IVHB status by canton
BMZ — the building mass index
Regime: IVHB Annex 1 no. 8.3 where the canton has joined, otherwise cantonal law. The building mass index (BMZ) puts the building volume above the determining terrain, in cubic metres, in relation to the countable parcel area: allowed volume = BMZ × parcel area. It is used mainly in French-speaking cantons and in individual zones where volume, not floor area, is the governing figure.
Source: IVHB Annex 1, no. 8 (lexfind.ch) · Checklist step 3: clarify the building zone and floor area ratio · Guide: IVHB status by canton
ÜZ — the building coverage ratio
Regime: IVHB Annex 1 no. 8.4 where the canton has joined, otherwise cantonal law. The building coverage ratio (ÜZ) limits the countable building area inside the projected facade line, not the floor area: allowed footprint = ÜZ × parcel area. It mainly governs how much of a parcel must stay unbuilt (green space, setbacks).
Source: IVHB Annex 1, no. 8 (lexfind.ch) · Guide: IVHB status by canton
GZ — the green space ratio
Regime: IVHB Annex 1 no. 8.5. The green space ratio (GZ) is the countable green area over the countable parcel area. Countable green area means natural and/or planted ground that is not sealed and not used for parking. The IVHB defines only the ratio, not the figure; the commune sets the figure, usually as a minimum share. Example: with 600 m² countable parcel area and 210 m² countable green area, GZ = 210 ÷ 600 = 0.35; if the building and zoning regulations require a GZ of 0.3, at least 0.3 × 600 = 180 m² of green area is needed. The calculator above treats the GZ as a minimum share: it shows the minimum green area required and, if you enter the existing green space, the gap to that minimum. Cantons that have not joined the IVHB regulate green space under their own law.
Source: IVHB Annex 1, no. 8 (lexfind.ch) · Guide: IVHB status by canton
Where to find your parcel's index value
The applicable index and its value are in the land-use plan — available online in the PLR cadastre and in the commune's own building and zoning regulations. alpflo computes from the value you read there and enter here; we make no claim about any specific parcel.
Source: PLR cadastre (cadastre.ch) · Glossary: PLR · Guide: how Switzerland measures a home
The four honesty states
Every fact in an alpflo register brief carries exactly one of these states.
Confirmed in an official Swiss register. Direct source.
Register queried; nothing on this parcel. The absence is documented.
Derived from a model or an API: real, but not directly from the register. Please verify.
Hit an edge case. Stated honestly at the boundary, never silently discarded.
Frequently asked questions about the buildability index
What's the difference between AZ and GFZ?
The formula is the same: countable floor area over parcel area. The name and the definition of the countable area differ: GFZ is the IVHB term, AZ is cantonal law.
Is the floor area ratio an IVHB term?
No. The IVHB defines the floor space index (GFZ); the floor area ratio (AZ) is cantonal law. Aargau, Obwalden, Schaffhausen, Uri and Zug joined but kept the AZ; cantons that have not joined apply their own law. The status of all 26 cantons is on the IVHB page.
Where do I find my parcel's buildability index?
In the PLR cadastre (the land-use planning theme) or your commune's own building and zoning regulations. Both are publicly available.
Does alpflo compute with real data about my parcel?
No. This calculator uses only the values you enter yourself — it makes no claim about any specific parcel.
Is the computed result a building permit?
No. Other rules — setbacks, height, storey count, noise-sensitivity level, density transfers — can further restrict what's actually buildable. For a binding answer, the communal building authority is responsible.
Read next
For a specific project, alpflo checks a building application's figures against the commune's provisions — every finding with its article, source and reliability. In writing within two working days, invoiced.
On request · invoiced · every fact with its source.