How to Calculate Floor Area Ratio: FAR and Floor-Area Limits

 

Floor area ratio, commonly shortened to FAR, compares counted floor area with lot area. It expresses how much floor area there is relative to the land, rather than how much of the ground is covered by a building. Calculating the ratio is straightforward once the correct area definitions are established.

The Floor Area Ratio Calculator calculates FAR and optionally compares counted floor area with a maximum ratio you provide. It performs arithmetic only; it does not identify local zoning limits or determine what spaces legally count.

Use the floor area ratio formula

The formula is FAR = total counted floor area / lot area. Both areas must use the same unit. If counted floor area is 15000 square feet and lot area is 10000 square feet, FAR is 15000 / 10000 = 1.5.

A FAR of 1.5 means counted floor area is 1.5 times lot area, equivalent to 150% of lot area. The ratio itself has no unit. Converting both areas consistently to square meters leaves the ratio unchanged.

Enter a worked example

Leave Area unit at Square feet (sq ft). Enter Lot area 10000 and Total counted floor area 15000. Leave Maximum FAR (optional) blank and select Calculate floor area ratio.

The results show Floor area ratio (FAR) 1.5 and counted floor area as a percentage of lot area of 150%. With no maximum entered, the calculator does not display a floor-area ceiling comparison.

Compare an entered maximum FAR

If the applicable maximum is known, calculate floor-area ceiling = maximum FAR x lot area. For a maximum FAR of 2 and lot area of 10000 square feet, the arithmetic ceiling is 20000 square feet.

Enter Maximum FAR (optional) 2 and calculate again. The difference between that ceiling and the counted 15000 square feet is 5000 square feet. Enter the maximum as a ratio, not a percentage: 2 means 2:1, not 2%.

A positive difference indicates arithmetic headroom under the entered ratio. Zero means the counted area equals the ceiling. A negative difference means it exceeds that ceiling. None of these results alone determines legal compliance or permission to build.

Check which floor area counts

The numerator must follow the applicable planning definition. Living area from a property listing may differ from the floor area used for FAR. Basements, parking, mechanical rooms, balconies, accessory buildings and voids may receive different treatment under local rules.

The lot-area denominator may also require a specific definition or adjustment. Consult the relevant code or planning authority before choosing the figures. The calculator does not apply exemptions, bonuses, transfers or parcel-specific provisions automatically.

Distinguish FAR from site coverage

FAR includes counted area across relevant levels and buildings. A multi-level building can have total floor area greater than the land area without covering more than the whole site at ground level. A 150% floor-area figure is therefore not 150% footprint coverage.

Different arrangements can produce the same FAR. For example, the same counted total might be distributed across fewer larger floors or more smaller floors. FAR alone does not determine the building's height, number of stories or footprint.

Keep the comparison within its limits

Setbacks, height limits, lot coverage, parking, access and environmental restrictions can constrain a project independently. A positive difference from the entered FAR ceiling is not necessarily additional buildable floor area.

Use local requirements and suitable professional advice when evaluating a real proposal. For basic area measurements, use the Square Footage Calculator, then confirm whether those areas belong in the planning calculation.

Changing the unit selector reinterprets the entered values rather than converting them. Keep both areas in one unit, retain unrounded figures for further calculations and remember that displayed decimals do not improve the accuracy of source measurements.