Floor Area Ratio Calculator
Floor area ratio, site coverage and how much floor area a site allows — the planning numbers that decide what can be built.
How much floor area the site allows.
How the floor area ratio calculator works
Floor area ratio is total floor area divided by site area. An FAR of 0.5 on a 600 m² site permits 300 m² of floor — across any number of storeys, which is what makes it different from site coverage.
Site coverage limits the building footprint instead. The two together shape what is possible: a high FAR with low coverage forces the building upward.
Formula: FAR = total floor area / site area
Worked examples
| Inputs | Result | Note |
|---|---|---|
| 600 m² site at FAR 0.5 | 300 | 300 m² of floor area |
| An existing 250 m² house | 0.417 | FAR 0.417, coverage 30% |
| A denser zoning | 900 | 900 m² — needs multiple storeys |
FAQFrequently asked questions
What is floor area ratio?
Total floor area divided by site area. An FAR of 0.5 on a 600 m² site allows 300 m² of floor, over any number of storeys.
How is it different from site coverage?
Coverage limits the footprint; FAR limits the total floor area. A site can have low coverage and high FAR — that is how towers happen.
Is it the same as plot ratio?
Yes. UK and Australian planning often calls it plot ratio or floor space ratio; the arithmetic is identical.
What counts as floor area?
It varies by jurisdiction — garages, balconies, basements and voids are treated differently everywhere. Check the local definition before relying on a number.
Is this planning advice?
No. It is arithmetic. The controls that apply to a specific site come from its planning scheme, and only the consent authority can confirm them.
Where these figures come from
- The Engineering ToolBox — material densities, coverage and unit data — bulk densities, concrete at 2,400 kg/m³, board and sheet sizes
- Cement Concrete & Aggregates Australia — concrete basics and yields — bag yields, density 2,400 kg/m³
- Australian Building Codes Board — the National Construction Code
Last checked: September 2026. Coverage rates and material sizes are typical manufacturer figures — check the product you buy.