Floor Area Ratio Calculator
A building’s floor area ratio from its gross floor area and lot size, or the floor area a given ratio allows on a lot, or the lot a floor area needs.
Result
Floor area ratio: 0.5
What counts as floor area is set by your zoning code.
- The ratio as a percentage
- 50%
https://calcgallery.com/real-estate/floor-area-ratio-calculator/
Results are arithmetic from the numbers you enter, not investment, lending, tax or valuation advice. The site supplies no rents, prices, cap rates or market data, and whether a deal is sound depends on facts no calculator can see. Read the full disclaimer
How to use the Floor Area Ratio Calculator
- Enter the building's gross floor area, every floor added together, and the lot's area.
- Read the floor area ratio, as a decimal and as a percentage.
- Or switch mode to find the floor area a ratio from your zoning code allows on a lot, or the lot a building of a given size needs.
The ratio
floor area ratio = gross floor area ÷ lot areafloor area = floor area ratio × lot arealot area = gross floor area ÷ floor area ratioThe two areas must be in the same unit, and the page converts square feet, square metres, acres and hectares before dividing, so a lot entered in acres and a building in square feet still give the right ratio.
What the ratio does not tell you
A floor area ratio says nothing about how the floor area is arranged. Lot coverage, setbacks, height limits and parking rules decide the shape a building can take, and together they may allow less floor area than the ratio alone. Check all of them with the local planning department.
With your numbers
- Floor area ratio = gross floor area ÷ lot area
Quick reference
What counts as floor area is set by your zoning code.
| Example | Result |
|---|---|
| 3,000 sq ft on a 6,000 sq ft lot | Floor area ratio: 0.5 |
| 21,780 sq ft on one acre | Floor area ratio: 0.5 |
| FAR 2.5 on a 10,000 sq ft lot | Gross floor area: 25,000 ft² |
| FAR 0.5 on a 7,500 sq ft lot | Gross floor area: 3,750 ft² |
| Lot for 25,000 sq ft at FAR 2.5 | Lot area: 10,000 ft² |
| 450 m² on a 600 m² lot | Floor area ratio: 0.75 |
Common questions about the Floor Area Ratio Calculator
- How do you calculate floor area ratio?
- Divide the building’s gross floor area by the area of its lot. A 3,000 square foot house on a 6,000 square foot lot has a FAR of 0.5. Some codes write the same thing as a percentage, 50%.
- What does a FAR of 1 mean?
- That the floor area equals the lot area. It could be a one-storey building covering the whole lot, a two-storey building covering half, or a four-storey building covering a quarter. The ratio limits the total floor area, not the footprint or the height, which zoning controls separately.
- What counts as gross floor area?
- Whatever your zoning code says. Codes differ on basements, attics, garages, balconies and whether walls are measured to the outside face. Measure the floor area the way the code defines it before comparing with its limit.
- What FAR is allowed on my lot?
- That is set by the zoning district your lot is in, and sometimes adjusted by overlays, bonuses or variances. The page states no limit. Take the figure from your local zoning code or planning department and enter it to see the floor area it allows.