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Floor Area Ratio Calculator.

Calculate floor area ratio from explicit floor and lot areas.

On-device calculationNo signup
01

Set your values

Results update as you type.

floorArea: 2,400

floorArea

0.0000
lotArea: 6,000

lotArea

0.0000
Ratio: 0.4

Ratio

0.0000
Ratio (%): 40

Ratio (%)

0.0000

Planning arithmetic only; enter explicit dimensions, areas, and elapsed times. No code, product, density, or design recommendation is inferred.

Use Cases

Zoning Compliance Check

Determine if your proposed building density meets local zoning regulations by comparing your calculated FAR with the maximum allowed FAR for your zone.

Example: If your lot is 5,000 sq ft and your building has 10,000 sq ft, FAR is 2.0. Check if your zone allows FAR 2.0.

Building Design Planning

Use FAR to plan the maximum floor area you can build on a given lot, helping you decide on the number of stories or building footprint.

Example: For a 10,000 sq ft lot with a max FAR of 1.5, you can build up to 15,000 sq ft total floor area.

Frequently Asked Questions

What is floor area ratio (FAR)?
Floor area ratio (FAR) is the ratio of a building's total floor area to the size of the lot it sits on. It is calculated by dividing the total floor area by the lot area. FAR is used in zoning to regulate building density.
How do I calculate floor area ratio?
To calculate floor area ratio, divide the total floor area (in square feet) by the lot area (in square feet). For example, if your building has 10,000 sq ft of floor area on a 5,000 sq ft lot, the FAR is 2.0.
What does a higher floor area ratio mean?
A higher FAR indicates more building floor area relative to the lot size, meaning denser development. For instance, an FAR of 3.0 allows three times the lot area in floor space, often seen in multi-story buildings.

Tips & Common Mistakes

Tips

  • Ensure both total floor area and lot area are in square feet before calculating; if they are in different units, convert them first.
  • Total floor area typically includes all floors of the building, including basements and attics if they are habitable, but check local definitions.
  • Lot area is the total land area within your property boundaries, not just the building footprint.
  • Use the calculated FAR to compare with your local zoning ordinance to see if your project is compliant.

Common Mistakes to Avoid

  • Using the building footprint instead of total floor area. The footprint is only the ground floor area, not the sum of all floors.
  • Forgetting to convert units. If your floor area is in square meters and lot area in square feet, the result will be incorrect.
  • Including non-habitable spaces like parking garages or mechanical rooms in the floor area when they are excluded by local zoning rules.

Last updated: August 13, 2026