Utilization ratio in Switzerland: AZ, BMZ and GZ explained simply
- Simon Käslin
- Jun 15
- 6 min read
Updated: 32 minutes ago
Land use ratios determine how much may be built on a plot, and they are therefore one of the most important levers for the value of that plot.
The utilisation ratio, the building mass ratio, the site coverage ratio and the green space ratio sound technical, but they follow a simple logic. They all relate the permissible building volume or the permissible area to the plot area.
Which ratio applies is set out in the building and zoning regulations of the municipality. Anyone who can read these ratios recognises early what is realistic on a plot. raumwert plus reviews these planning law options as part of the property analysis.
Table of contents
How much are you allowed to build on your property?
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1. What are land use ratios?
Land use ratios (the utilisation ratio, the floor space ratio and the building mass ratio) are planning law indicators that set out how intensively a plot may be developed. They relate a permissible size, such as an area or a volume, to the plot area. Municipalities use them to control building density and to keep the character of a place consistent.
For clients they are central, because they define the scale of what is possible. Before an idea takes shape, the ratio decides how much may be built at all.
The Intercantonal Agreement on the Harmonisation of Building Terminology (IVHB) has standardised many of these terms across Switzerland, even though not all cantons have progressed equally far.
2. What is the utilization ratio in Switzerland?
The utilization ratio in Switzerland (AZ) describes the ratio of the chargeable gross floor area to the eligible plot area. An AZ of 0.5 means, in simplified terms, that on a plot of 800 square metres around 400 square metres of chargeable gross floor area may be built.
The AZ was the most common land use ratio for a long time. Many cantons and municipalities have since moved to other ratios, because the AZ is complicated to apply. It is nevertheless still widespread and decisive for many plots.
3. What is the building mass ratio (BMZ)?
The building mass ratio relates the permissible building volume to the plot area. It is stated in cubic metres per square metre. A BMZ of 3.0 means that three cubic metres of building volume may be built on one square metre of plot area.
The BMZ has the advantage that it limits the actual volume and works independently of the number of storeys. It is increasingly common in the canton of Zurich and in other cantons, because it is simpler and more transparent than the utilisation ratio.
4. What is the site coverage ratio (UeZ)?
The site coverage ratio describes what share of the plot area may be built on. A UeZ of 0.3 means that at most thirty percent of the plot area may be covered by buildings.
It therefore governs the footprint of the buildings, not their height or their volume. Combined with further rules such as the number of storeys and the permitted height, this defines the building that is possible.
5. What is the green space ratio (GZ)?
The green space ratio sets out what share of the plot has to be kept as green or open space. A GZ of 0.3 means that at least thirty percent of the area must be planted and left unsealed.
It therefore acts as the counterpart to site coverage and secures quality in the outdoor space. In denser zones in particular the green space ratio is gaining importance, because it contributes to living quality and to the microclimate.
6. Which ratio applies to my plot?
Which land use ratios are decisive is set out in the building and zoning regulations and in the zoning plan of the municipality concerned. Different ratios apply depending on the zone and the canton, and often several apply at the same time. A plot may, for example, be subject to a building mass ratio and a green space ratio at once.
It is therefore not enough to know a single figure. What is decisive is the interplay of all the rules. That is exactly what is examined systematically in a site analysis.
7. Which areas count towards the ratio?
A frequent source of misunderstanding is the question of which areas are counted. Not every area counts towards the chargeable gross floor area. Depending on the regulations, basement rooms, plant areas or certain ancillary rooms are excluded.
These counting rules often decide how much can actually be realised on a plot. Anyone who does not know them precisely will over or underestimate the potential.
8. Worked examples
Two simple examples show the logic.
Ratio | Value (example) | Result on 800 m² |
Utilisation ratio (AZ) | 0.5 | 400 m² chargeable gross floor area |
Building mass ratio (BMZ) | 3.0 | 2,400 m³ building volume |
Site coverage ratio (UeZ) | 0.3 | max. 240 m² built-up area |
Green space ratio (GZ) | 0.3 | min. 240 m² green space |
Worked examples for a plot of 800 m². What is always decisive is the interplay of all the ratios in your municipality.
Utilisation ratio: plot of 800 square metres, AZ 0.5. Permissible chargeable gross floor area: 800 times 0.5 gives 400 square metres.
Building mass ratio: plot of 800 square metres, BMZ 3.0. Permissible building volume: 800 times 3.0 gives 2400 cubic metres.
These figures are the starting point for any feasibility consideration. How a concrete concept develops from them is covered in the article Feasibility study and volume study.
9. Why are the ratios decisive for the value of a plot?
The value of a plot depends heavily on how much may be built on it. Two plots of the same size can be worth very different amounts if their land use ratios differ. Anyone who buys a plot is essentially buying this development right.
That is why checking the ratios before a purchase is so important. How a land purchase is reviewed as a whole is covered in the article Buying land in Switzerland.
10. Which mistakes happen most often?
The most common mistake is to look at one ratio in isolation and to derive a potential from it too quickly. In practice several rules work together, and setbacks, heights or green space shares further limit what is possible.
Another mistake is to overlook the counting rules. Anyone who assumes that every area counts the same will miscalculate. Both mistakes lead to false expectations that have to be corrected expensively later on.
11. What is the floor space ratio (GFZ)?
The floor space ratio relates the sum of all floor areas to the eligible plot area. It therefore describes how much floor area is permitted on a plot in total. The calculation logic matches that of the other land use ratios.
It differs from the utilisation ratio above all in which areas are counted. The utilisation ratio is based on the chargeable gross floor area, from which certain rooms can be excluded. Because the counting rules diverge, the two ratios cannot be compared directly.
Since the harmonisation of building terminology many municipalities use the floor space ratio instead of the utilisation ratio. Which ratio applies to your plot, and which areas are counted, is set out in the building and zoning regulations of the municipality. Check this basis before you derive a potential from a single ratio.
12. Frequently asked questions about land use ratios
What is the utilisation ratio?
The utilisation ratio (AZ) describes the ratio of the chargeable gross floor area to the plot area. An AZ of 0.5 allows around 400 square metres of chargeable gross floor area on 800 square metres.
How do I calculate the utilisation ratio?
You multiply the eligible plot area by the utilisation ratio. Example: 800 square metres times an AZ of 0.5 gives 400 square metres of permissible chargeable gross floor area.
What is the difference between the utilisation ratio and the building mass ratio?
The utilisation ratio limits the floor area, the building mass ratio limits the building volume in cubic metres per square metre. The BMZ is independent of the number of storeys and is regarded as more transparent.
Which areas count towards the utilisation ratio?
That depends on the regulations. Basements, plant areas and certain ancillary rooms are often excluded from the count. The exact rules are set out in the municipal building and zoning regulations.
Where do I find the land use ratio for my plot?
In the building and zoning regulations and in the zoning plan of the municipality. Several ratios often apply at the same time, which is why a professional review is worthwhile.
13. How a site analysis helps
A site analysis examines all the relevant ratios and rules together and shows what is realistically possible on a plot. That protects against bad purchases and against designs that fail at planning law limits.
raumwert plus carries out this review as an independent site analysis, so that you know the potential and the limits of your plot before you invest.
How much are you allowed to build on your property?
A brief, independent assessment provides clarity and shows whether potential remains untapped.
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