Floor Area Ratio Calculator

Calculate FAR, compare building density with a zoning limit, and estimate remaining development capacity.

FAR and Zoning Density Calculator
Enter total counted floor area and lot area in the same unit, with an optional maximum FAR for a preliminary compliance check.

About floor area ratio

Floor area ratio, usually shortened to FAR, compares the total counted floor area of buildings with the area of the development lot. The formula is total floor area divided by lot area. Because both measurements use the same square unit, the result is dimensionless. A 2,500-square-foot house on a 5,000-square-foot lot has an FAR of 0.5, while a 50,000-square-foot office building on a 20,000-square-foot lot has an FAR of 2.5. FAR is not the same as building coverage. Coverage compares only the building footprint with the lot, while FAR can include floor area on every counted story. An FAR above 1 is therefore common in multi-story development. The percentage shown by this calculator is simply FAR multiplied by one hundred; it expresses total floor area relative to lot area and should not be interpreted automatically as footprint coverage. When a maximum FAR is supplied, the calculator multiplies that limit by lot area to find the maximum allowed floor area. It then compares the proposed total with that allowance. A positive remainder indicates theoretical floor-area capacity, while an excess indicates how much counted floor area would need to be removed or otherwise addressed. Other controls can prevent use of the full theoretical capacity, including height limits, setbacks, lot coverage, open-space rules, parking, daylight planes, design review, and environmental constraints. The most important input question is what the local zoning code counts. Jurisdictions differ on basements, garages, mechanical rooms, balconies, mezzanines, attics, accessory structures, transfer areas, and public rights-of-way. Gross floor area on architectural drawings may not equal zoning floor area. Lot area may also need adjustment for dedications, submerged land, or portions outside the zoning lot. Use official surveys and the definitions in the current ordinance. This tool is useful for quick feasibility studies, comparing massing options, checking arithmetic, and communicating density. It does not establish a development right or guarantee permit approval. Overlay districts, bonuses, affordable-housing programs, heritage controls, conditional uses, and existing nonconformities can alter the effective limit. Document every inclusion and exclusion, keep floor and lot units consistent, and have the calculation confirmed by the planning authority or a qualified land-use professional before relying on it for acquisition, design, financing, or permitting.

Floor area ratio examples

Development scenarioCalculated FARDensity interpretation
2,500 sq ft house on a 5,000 sq ft lotFAR 0.5At a 0.6 limit, another 500 square feet of counted floor area is theoretically available.
15,000 sq ft apartment building on a 10,000 sq ft lotFAR 1.5The total floor area equals one and one-half times the lot area.
50,000 sq ft office on a 20,000 sq ft lotFAR 2.5At a 3.5 limit, the maximum counted floor area is 70,000 square feet.
80,000 sq ft mixed-use building on a 25,000 sq ft lotFAR 3.2The same ratio results whether both areas use square feet or square meters.

How to calculate FAR

  1. Determine the zoning-defined total floor area from current project drawings.
  2. Obtain the official zoning-lot area and use the same square unit for both inputs.
  3. Enter the local maximum FAR when you want a preliminary compliance comparison.
  4. Select Calculate FAR and review the ratio, percentage, and development capacity.
  5. Verify inclusions, exclusions, overlays, and other development controls with the planning authority.

Floor area ratio FAQ

What does an FAR of 2.0 mean?

It means total counted floor area equals twice the lot area. That area might be arranged as two full-lot stories, four half-lot stories, or another form allowed by other controls.

Is FAR the same as lot coverage?

No. FAR counts floor area across stories, while lot coverage generally considers the ground-level footprint. A project must often comply with both limits independently.

Do basements and parking count toward FAR?

The answer depends on local definitions and sometimes on elevation, use, or design. Consult the applicable zoning ordinance rather than assuming those spaces are included or excluded.

Can remaining FAR always be built?

No. Height, setbacks, coverage, parking, design standards, easements, and site conditions may prevent full use of theoretical floor-area capacity. The remainder is only an arithmetic comparison.

Must floor area and lot area use square feet?

No. Both may use square meters or another consistent area unit because the units cancel in the ratio. Never divide measurements expressed in different units without converting first.