Floor Area Ratio Calculator

Calculate floor area ratio from lot and building size

The Floor Area Ratio Calculator helps you compare a building's floor area with the size of the lot it sits on. Enter the lot area and the floor area for each level. The calculator totals the floors, subtracts any floor area you enter as excluded, and divides the counted floor area by the lot area. The result is the floor area ratio, often shortened to FAR. You can also enter a zoning FAR limit to estimate maximum floor area and remaining capacity.

The calculator includes a separate building footprint input to estimate lot coverage. FAR and lot coverage describe different things: FAR compares all counted floors with the lot, while lot coverage compares the building's ground footprint with the lot. A multi-story building can have floor area several times larger than its footprint, so these two values should not be confused.

Use the tool for early planning, design comparisons, zoning research, or a quick explanation of FAR. It does not determine whether a project complies with a zoning code. Local rules define what floor areas count, how lot area is measured, which bonuses or exclusions apply, and what other limits control a building. Verify the applicable zoning text and speak with the planning department or a qualified design professional before relying on a result.

How to use the FAR calculator

Choose square feet or square metres. Enter the total zoning lot area, then add the floor area for each building level. Use the area counted under the local zoning definition when you know it. If the building has floors of different sizes, enter each floor separately. Add or remove floor rows with the controls so the total reflects the actual building or a proposed design.

Enter any floor area that should be excluded from the FAR calculation according to your local rules. The calculator subtracts this amount from the gross floor area total. Exclusions vary widely, so enter zero unless you know which specific spaces your jurisdiction excludes and how it measures them. Do not guess based on a rule from another city or project.

Enter the building footprint to estimate lot coverage. This is usually the area where the building meets the ground, but local definitions can treat projections, covered spaces, or accessory structures differently. For a zoning comparison, use the footprint definition that applies to the relevant ordinance.

If you know the maximum permitted FAR, enter it in the zoning limit field. The calculator multiplies that FAR by the lot area to estimate maximum counted floor area, then compares the current counted area to that number. A positive remaining value indicates arithmetic space under the entered limit; a negative value indicates the entered floor area exceeds it. Other zoning limits may still prevent construction even when this estimate shows remaining capacity.

Floor area ratio formula

FAR is a ratio of counted building floor area to lot area. First add the floor areas for all included stories and buildings on the lot. Subtract only the areas that the applicable zoning rules exclude. Divide that counted floor area by the zoning lot area. FAR has no unit because both values use the same area unit and cancel out.

For example, if a lot is 5,000 square feet and counted building floor area is 3,000 square feet, FAR is 3,000 ÷ 5,000, or 0.60. If the same lot had 10,000 square feet of counted area across multiple floors, its FAR would be 2.0. The ratio does not tell you the building's height, number of stories, shape, or placement on the lot.

• Gross floor area = sum of floor areas entered for all levels
• Counted floor area = gross floor area − locally excluded floor area
• Floor area ratio (FAR) = counted floor area ÷ lot area
• Maximum floor area = lot area × permitted FAR
• Remaining floor area = maximum floor area − counted floor area
• Lot coverage = building footprint ÷ lot area × 100%

Worked example using a 5,000 square foot lot

Suppose a parcel is 5,000 square feet and a proposed building has three levels measuring 1,500, 1,500, and 1,000 square feet. Gross floor area is 4,000 square feet. If local rules allow 200 square feet to be excluded and that exclusion has been confirmed, counted floor area is 4,000 − 200 = 3,800 square feet. FAR is 3,800 ÷ 5,000 = 0.76.

If the entered maximum permitted FAR is 1.0, maximum counted floor area would be 5,000 × 1.0 = 5,000 square feet. The arithmetic remaining area is 5,000 − 3,800 = 1,200 square feet. That does not mean the property can automatically add 1,200 square feet. Height, setbacks, lot coverage, use, parking, open space, building code, access, and other rules can limit the design.

If the building footprint is 1,500 square feet, lot coverage is 1,500 ÷ 5,000 × 100%, or 30%. This percentage is separate from the FAR of 0.76. The example shows how a building can have several floors while occupying a smaller portion of the lot at ground level.

FAR versus lot coverage

Floor area ratio measures building floor area relative to lot area. Lot coverage measures how much of the lot is covered at ground level by a building footprint. A one-story building with a 2,000 square foot footprint on a 5,000 square foot lot could have an FAR of 0.40 and lot coverage of 40%, before local exclusions or other structures are considered.

A two-story building with the same 2,000 square foot footprint might have 4,000 square feet of floor area and a FAR of 0.80, while lot coverage remains about 40%. The additional floor area increases FAR without increasing the footprint. This is why zoning codes often regulate FAR and lot coverage separately, alongside height, yards, setbacks, and open space.

The calculator uses the footprint value you enter and does not infer it from the floor areas. Enter the actual or proposed ground-level footprint. If the first floor is larger than upper levels, or a structure has multiple disconnected sections, calculate the footprint according to the local definition.

What counts as floor area?

The phrase floor area can have different meanings in different zoning codes. A jurisdiction may define it using gross floor area, floor area measured to exterior walls, or a special formula. Certain spaces might be included or excluded, such as parking, mechanical rooms, basements, balconies, stairwells, accessory structures, or covered areas. The exact list and measurement method are local legal definitions, not universal architectural rules.

The calculator makes exclusions user-entered because it cannot determine which spaces qualify in your location. If a space is excluded under a local rule, subtract only the amount calculated under that rule. If the code applies limits, conditions, or partial exclusions, ask a planning official or design professional how to measure them. Applying an exclusion incorrectly can materially change the apparent FAR.

For multiple buildings on one zoning lot, some regulations calculate the combined floor area across those buildings. The New York City Zoning Resolution, for example, defines FAR using total floor area on a zoning lot divided by the lot area. Other cities may use different definitions and lot boundaries. Read the governing rules for the parcel rather than assuming every jurisdiction uses identical wording.

Find the maximum floor area from an FAR limit

If a zoning district permits a maximum FAR, multiply that value by the lot area to find the arithmetic maximum floor area under that ratio. For a 7,200 square foot lot with an entered FAR limit of 0.5, the result is 3,600 square feet. At an FAR limit of 2.0, it is 14,400 square feet. The lot area and FAR must use the same zoning basis for this calculation to make sense.

A maximum FAR is not necessarily a guaranteed building size. A design may be constrained by a maximum height, required yards, setbacks, lot coverage, street walls, parking, access, open space, daylight rules, environmental restrictions, or other zoning provisions. Some places allow bonuses, transfers, or special permits; others set different limits by use or building type.

Use the maximum FAR field to compare a scenario, not to confirm development rights. Check zoning maps and text for the exact parcel, applicable use, overlays, exceptions, and any required approvals. A local planner can help interpret how a zoning lot is defined and which floor areas count.

Plan multiple floors and changing footprints

Many buildings do not have identical floor plates. Upper stories may step back, additions may cover only part of a floor, and a building may include several wings. Enter each floor's area separately to get a more accurate total. If a floor contains a large opening or atrium, determine whether the local FAR definition counts that space and enter the appropriate area.

For two or more buildings on one lot, add every relevant floor in the total. If the zoning rule treats each lot separately or allows floor area transfers, the calculator's basic lot-level ratio may not capture the legal calculation. The same is true for shared lots, condominium parcels, merged zoning lots, or development rights. Use the correct legal lot area and floor-area definition for your case.

Using metric area measurements

The calculator can work in square feet or square metres. Switch units and enter all lot, floor, exclusion, and footprint areas in the selected unit. FAR stays the same because the numerator and denominator convert by the same area factor. A 500 square metre building on a 1,000 square metre lot has the same FAR as 5,381.96 square feet on a 10,763.91 square foot lot: 0.5.

Keep measurement units consistent within an estimate. Do not enter the lot in square metres and floors in square feet. If a survey or building plan uses dimensions rather than area, calculate each rectangular floor as length times width, then add sections with different shapes. Use measured plans where possible and retain the source dimensions for review.

Common FAR calculation mistakes

One common mistake is using only the building footprint as the numerator when a structure has multiple floors. FAR usually compares total counted floor area on all levels with lot area, subject to local definitions. Another is dividing by the building area instead of the lot area. The formula is counted floor area divided by zoning lot area.

A second mistake is assuming every basement, garage, balcony, mechanical room, or stair is automatically excluded. Exclusions differ by jurisdiction and may depend on location, design, or use. Do not subtract an area simply because another city excludes it. Enter an exclusion only after confirming the applicable zoning rule.

A third mistake is treating remaining FAR as permission to build. The ratio is only one planning control. Height, setbacks, lot coverage, open space, use, fire access, building code, utilities, and site conditions can change what is feasible. Always use the current local zoning text and parcel information.

Frequently asked FAR questions

What is floor area ratio? FAR is the ratio of counted building floor area to lot area. How do I calculate FAR? Add included floor areas, subtract applicable exclusions, and divide by lot area. What does FAR 1.0 mean? As a simple ratio, counted floor area equals lot area, although local rules determine what counts and how a building may be arranged.

What is FAR 2.0 on a 5,000 square foot lot? It represents 10,000 square feet of counted floor area under the simple multiplication, before applying any local rules or other constraints. Does FAR include all floors? Often it uses the sum of counted floor area across levels, but the code definition controls. Is FAR the same as lot coverage? No. FAR considers floor area across the building; lot coverage compares ground footprint with lot area.

How do I find allowable floor area? Multiply the applicable permitted FAR by the relevant zoning lot area. Can I build the remaining floor area shown? Not necessarily. Other zoning controls and approvals may limit the design, and exclusions or lot definitions must be confirmed with local authorities.

Use the result as a planning estimate

A useful FAR estimate starts with the right lot area, a floor-by-floor area schedule, and the exact local definition of counted floor area. Enter those values consistently, use confirmed exclusions, and compare the result with the applicable FAR limit. Check lot coverage separately and review the rest of the zoning controls before judging a design.

Keep a record of where your area measurements and zoning assumptions came from. If a project is moving toward permitting, ask the local planning department or a qualified architect, land-use planner, or surveyor to verify the calculation. This calculator is designed to make the arithmetic clear; local zoning rules determine the legal answer.