Floor area ratio calculator
Find how much floor area a zoning FAR allows on a lot, or a building's floor area ratio. Add the number of storeys to see the average floor plate and how much of the lot it covers.
See your design as an AI render — freeUse the same unit for both areas: square feet, square meters, anything.
- As a percentage (FSI %)
- 250%
- Average floor plate
- 5,000 sq ft
- Lot coverage
- 50%
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How to calculate floor area ratio
Floor area ratio (FAR) compares a building's total floor area with the size of its lot.
- 1
Add up the gross floor area
Sum the floor area of every storey that counts under your zoning code. Codes differ on what is excluded (basements, parking, mechanical floors, balconies), so use your code's definition.
- 2
Divide by the lot area
FAR = gross floor area ÷ lot area. An 18,000 sq ft building on a 12,000 sq ft lot has a FAR of 1.5. Both areas must use the same unit; the ratio itself has none.
- 3
Or work out the maximum floor area
Multiply the permitted FAR by the lot area. A FAR limit of 2.5 on a 10,000 sq ft lot allows up to 25,000 sq ft of floor area.
- 4
Check it against height and coverage
The same floor area can be tall and slim or low and wide. 25,000 sq ft over five storeys is a 5,000 sq ft floor plate covering 50% of the lot; height limits, setbacks and coverage limits decide the shape.
What a FAR looks like on a 10,000 sq ft lot
The same math as the calculator: floor area = FAR × lot; coverage = floor plate ÷ lot.
| FAR | Floor area | Example |
|---|---|---|
| 0.5 | 5,000 sq ft | 1 storey(s), 50% lot coverage |
| 1 | 10,000 sq ft | 2 storey(s), 50% lot coverage |
| 2 | 20,000 sq ft | 4 storey(s), 50% lot coverage |
| 4 | 40,000 sq ft | 8 storey(s), 50% lot coverage |
| 1 | 10,000 sq ft | 1 storey(s), 100% lot coverage |
| 1 | 10,000 sq ft | 4 storey(s), 25% lot coverage |
Frequently asked questions
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