Calculate Buildable Floor Area
With AZ, GFZ, BMZ, or ÜZ 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.
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, or ÜZ.
- 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 and the remaining reserve 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
The floor area ratio (AZ) and the floor space index (GFZ) put the chargeable floor area in relation to the parcel area: allowed floor area = index value × parcel area. Depending on the canton, the same concept is called AZ or GFZ; the harmonized building terminology (IVHB) groups both under one utilization index.
Source: Spatial Development ARE (are.admin.ch) · Glossary: floor area ratio
BMZ — the building mass index
The building mass index (BMZ) puts the allowed building volume, in cubic metres, in relation to the 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: Spatial Development ARE (are.admin.ch) · Checklist step 3: clarify the building zone and floor area ratio
ÜZ — the building coverage ratio
The building coverage ratio (ÜZ) limits the building's footprint, not its floor area: allowed footprint = ÜZ × parcel area. It mainly governs how much of a parcel must stay unbuilt (green space, setbacks).
Source: Land-use planning, Canton of Zurich (zh.ch) · See what zoning data looks like in the sample report
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
The four honesty states
Every fact in an alpflo report carries exactly one of these four states; this calculator itself uses only your own entries (see the note above) — the states show what you'd find in a real report.
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?
None in the calculation — both put the chargeable floor area in relation to the parcel area. The name differs by canton, or by the harmonized terminology (IVHB).
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.
First check the public sample report — a complete alpflo report with all four states, no signup. Then create your own report for a Swiss address in the app.
No subscription · CHF 49 per report · the sample report stays free.