Floor Area Ratio Calculator
Work out the floor area ratio (FAR) and lot coverage for a property. Enter the lot area, the building footprint and number of floors, and your zoning limits, and get the gross floor area, the FAR, the lot coverage, the maximum floor area allowed and how much is left to build — with a zoning check, by-floors and by-FAR tables, and a downloadable PDF.
| Floors | Gross floor area | FAR | vs limit |
|---|---|---|---|
| Enter a lot to compare | |||
| Allowed FAR | Max floor area | Remaining | vs built |
|---|---|---|---|
| Enter a lot to compare | |||
How to use the floor area ratio calculator
Four quick steps turn your lot and building size into floor area ratio, lot coverage and how much more you can build — with a zoning check, by-floors and by-FAR tables, a chart and a downloadable report.
Enter the lot area
Give the parcel size in square feet — it’s on the plat, deed or county assessor record.
Describe the building
Enter the building footprint and the number of floors that count toward floor area.
Add zoning limits
Pick a preset or enter your maximum FAR and lot coverage — or set 0 to skip the check.
Read results & save a PDF
Get floor area, FAR, coverage, what’s allowed and what’s left — then download a report.
How floor area ratio is calculated
Floor area ratio compares all the floor space in a building to the size of its lot, while lot coverage looks only at the ground floor footprint. Here is the exact math the calculator runs.
Worked example — 7,500 sq ft lot, 1,800 sq ft footprint, 2 floors, max FAR 0.5, max coverage 40%
Gross floor area: 1,800 × 2 = 3,600 sq ft · FAR: 3,600 ÷ 7,500 = 0.48 · Coverage: 1,800 ÷ 7,500 = 24%
Max floor area: 0.5 × 7,500 = 3,750 sq ft · Left: 3,750 − 3,600 = 150 sq ft
Max footprint: 40% × 7,500 = 3,000 sq ft · Left: 3,000 − 1,800 = 1,200 sq ft · Lot: 7,500 ÷ 43,560 ≈ 0.17 acres
FAR 0.48 and 24% coverage — within both limits, with 150 sq ft of floor area still allowed.
Floor area ratio reference charts
Handy lookups for how adding floors changes FAR, how much different FAR limits allow, and what the calculator’s presets mean on a 7,500 sq ft lot.
| Floors | Gross floor area | FAR | vs 0.5 limit |
|---|---|---|---|
| 1 | 1,800 sq ft | 0.24 | OK |
| 2 | 3,600 sq ft | 0.48 | OK |
| 3 | 5,400 sq ft | 0.72 | Over |
| 4 | 7,200 sq ft | 0.96 | Over |
| 5 | 9,000 sq ft | 1.20 | Over |
Adding a floor doesn’t change lot coverage, but it adds the full footprint to floor area.
| Allowed FAR | Max floor area | Remaining | vs built |
|---|---|---|---|
| 0.35 | 2,625 sq ft | over 975 | over |
| 0.50 | 3,750 sq ft | 150 sq ft | fits |
| 0.75 | 5,625 sq ft | 2,025 sq ft | fits |
| 1.00 | 7,500 sq ft | 3,900 sq ft | fits |
| 1.50 | 11,250 sq ft | 7,650 sq ft | fits |
| 2.00 | 15,000 sq ft | 11,400 sq ft | fits |
Max floor area = allowed FAR × lot area.
| Preset | Max FAR · coverage | Max floor area | Max footprint |
|---|---|---|---|
| Low | 0.5 · 40% | 3,750 sq ft | 3,000 sq ft |
| Med | 0.75 · 50% | 5,625 sq ft | 3,750 sq ft |
| High | 1.0 · 60% | 7,500 sq ft | 4,500 sq ft |
| Dense | 2.0 · 70% | 15,000 sq ft | 5,250 sq ft |
Presets are examples only — your actual limits come from your local zoning code.
What the floor area ratio calculator gives you
Three numbers about your lot and building give you a quick zoning picture.
FAR at a glance
Who uses a floor area ratio calculator
From an addition to a new build or a land purchase, the same math shows what a lot can hold.
Wants to know how much more floor area the lot allows before talking to an architect.
- Enter current footprint
- Check floor area left
- Confirm with zoning
Comparing lots and wants a quick read on how big a home or building each one could hold.
- Try different FAR limits
- Compare floors
- Save a PDF per lot
Testing massing options and needs FAR and coverage checks before drawing plans.
- Balance floors vs footprint
- Watch coverage cap
- Share with the client
Tips for working with FAR and lot coverage
Zoning rules are local and detailed — these habits keep your plans on track.
Floor area ratio calculator FAQ
Quick answers about floor area ratio, lot coverage, zoning limits and how much you can build.
Floor area ratio is the total floor area of a building divided by the area of its lot. It’s a zoning tool that limits how much building can go on a parcel.
A home with 3,600 sq ft of floor area on a 7,500 sq ft lot has a FAR of 0.48.
Multiply the building footprint by the number of floors to get the gross floor area, then divide by the lot area.
For a 1,800 sq ft footprint on 2 floors, that is 3,600 sq ft. On a 7,500 sq ft lot, 3,600 ÷ 7,500 = 0.48.
FAR counts the floor area on every story, while lot coverage counts only the ground footprint as a share of the lot.
The example home has a FAR of 0.48 but lot coverage of just 24%, because its 1,800 sq ft footprint covers about a quarter of the 7,500 sq ft lot.
Multiply your lot area by the maximum FAR your zoning allows. With a 0.5 limit, a 7,500 sq ft lot allows 3,750 sq ft of floor area.
If 3,600 sq ft is already built, about 150 sq ft is left. Lot coverage, height and setback rules can limit you too.
A FAR of 1.0 means the total floor area equals the lot area. That could be one story covering the whole lot, two stories over half of it, or four stories over a quarter.
On a 7,500 sq ft lot, a FAR of 1.0 allows 7,500 sq ft of floor area.
Add the footprint again and divide by the lot area. A third floor on the example home makes 5,400 sq ft and a FAR of 0.72.
That is over a 0.5 limit by 1,650 sq ft, but fits under a 0.75 limit.
It depends on your local zoning code. Many codes count every enclosed story, but basements, garages, attics and covered porches may be counted in full, in part or not at all.
Check how your district measures gross floor area before relying on the result.
FAR limits vary widely by city and zoning district. Low-density residential zones often allow lower ratios, while urban and mixed-use districts allow much higher ones.
The calculator’s presets run from 0.5 with 40% coverage to 2.0 with 70% coverage as examples only — your actual limits come from your local zoning code.
Planning estimate only — confirm with your zoning office. This calculator works in US units (square feet, acres) and uses FAR = gross floor area ÷ lot area and lot coverage = footprint ÷ lot area. How floor area is measured — which stories, basements, garages, attics and covered porches count — and the FAR, coverage, height and setback limits are set by your local zoning code and vary by district and overlay. The presets shown are illustrative. Confirm everything with your planning or zoning department before you design, buy or build.