Floor Area Ratio Calculator: FAR & Floor-Area Limit
Calculate floor area ratio (FAR) by dividing counted floor area by lot area. Optionally enter a maximum FAR to compare the same floor-area definition against that limit. The result is arithmetic, not a zoning approval or a determination of what floor area legally counts.
How to calculate floor area ratio
FAR = total counted floor area / lot area. Add the floor area that counts under the applicable local definition across the relevant buildings and levels, then divide by the applicable lot area. The result has no unit when both areas use the same measurement unit.
FAR 1.5 means counted floor area is 1.5 times lot area, or 150% of lot area. It does not mean that 150% of the site is covered by the ground-floor footprint. FAR is also called floor space ratio or floor space index in some jurisdictions, but definitions can differ.
Worked example
Leave Area unit at Square feet (sq ft). Enter Lot area 10000 and Total counted floor area 15000. Select Calculate floor area ratio. FAR is 15000 / 10000 = 1.5, and counted floor area is 150% of lot area.
Enter Maximum FAR (optional) 2 and calculate again. The floor-area ceiling from that number is 2 x 10000 = 20000 sq ft. The difference is 20000 - 15000 = 5000 sq ft. This is an arithmetic comparison only, not permission to add 5000 sq ft.
What counts as floor area?
Do not assume that a real-estate listing's living area, gross internal area or external building area matches the definition used for FAR. Local rules may treat basements, parking, mechanical rooms, balconies, voids and accessory buildings differently.
The appropriate lot-area definition may also require adjustments. Use the relevant code or planning authority's definition for both numerator and denominator. The calculator cannot determine exemptions or resolve whether a particular space counts.
Compare a maximum ratio carefully
When you provide a maximum, floor-area ceiling = maximum FAR x lot area. Subtract your entered counted area to see the difference. A negative result indicates that the counted area is above that entered ceiling; it does not by itself establish a legal violation.
A blank maximum means no comparison is performed. A zero maximum is a real numeric input and produces a zero ceiling. Make sure the maximum applies to the parcel, use and circumstances being considered. Bonuses, transfers or exceptions may require separate review.
FAR does not determine a building layout
The same FAR can result from different arrangements of floor area. A one-level building with a larger footprint and a multi-level building with a smaller footprint may have the same counted total. FAR alone cannot determine height, number of stories or site coverage.
Setbacks, height limits, lot coverage, parking, access, environmental restrictions and other requirements can limit a project independently. This calculator does not assess development feasibility or replace professional planning advice. For basic room or parcel geometry, use the Square Footage Calculator.
For a step-by-step walkthrough, read How to Calculate Floor Area Ratio: FAR and Floor-Area Limits.
Limits and privacy
Lot area must be positive; counted floor area may be zero. Both are limited to 1000000000000 in the selected unit. An optional maximum FAR may range from 0 to 1000. These are software limits, not planning standards. Results use floating-point arithmetic and display up to six decimal places, with scientific notation for tiny or very large values.
Calculations run locally in your browser. This calculator does not save or transmit parcel measurements. The hosting website may use separate analytics or advertising services.
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