Floor Area Ratio Calculator

FAR Calculator: Floor Area Ratio, Coverage and Compliance

Floor area ratio is the single number that decides how much building a plot can hold. This FAR calculator works it out from the plot area and the total floor area you’re planning, then checks the result against the zoning caps you enter. It also returns ground coverage, permissible floor area, remaining allowance, and compliance status in plain language.

Enter the plot area directly or as length by width. Add the ground floor footprint, how many upper floors, and whether a basement or stilt counts toward FAR. The tool handles the arithmetic, including the case where basement area exists but sits outside the FAR calculation. Costs come through as construction, land, and total, with a cost-per-FAR-unit figure at the end. Metric and imperial units switch cleanly.

How to Use the FAR Calculator

1. Pick the unit system: metric (m² / m) or imperial (ft² / ft).

2. Choose how to enter the plot. Direct area or length × width.

3. Enter the plot area, or the two dimensions.

4. Type the ground floor footprint.

5. Set how many upper floors the building has.

6. Choose whether upper floors match the footprint or use a custom area.

7. Add basement or stilt area if it exists, and decide whether it counts toward FAR.

8. Enter the zoning limits, then the construction and land costs.

The Summary tab shows FAR, coverage, compliance, and cost in one card. Detailed Breakdown lists every area and ratio behind the result.

How the FAR Calculator Formula Works

FAR is total floor area divided by plot area. Coverage is the ground floor footprint as a percentage of the plot.

Formula: Plot area = Length × Width (dimensions mode)
Formula: Total built-up area = Footprint + (Upper floors × Upper floor area) + Basement
Formula: FAR-counted area = Footprint + Upper total + (Basement if included)
Formula: FAR = FAR-counted area ÷ Plot area
Formula: Ground coverage = (Footprint ÷ Plot area) × 100
Formula: Permissible area = Max FAR × Plot area
Formula: FAR utilisation = (FAR ÷ Max FAR) × 100
Formula: Remaining allowance = Permissible area − FAR-counted area

Basement handling is the part that surprises people. Many zoning codes exclude basement and stilt parking from FAR entirely. Others include it. The calculator gives you a toggle so the same building can produce two different FAR figures depending on the local rule.

Compliance is a simple comparison. If FAR is above the max, or coverage is above the max, the result is flagged. If both caps are met, it passes. If no caps are entered, the tool says limits were not specified and skips the check.

Cost runs on the built-up area, not the FAR-counted area. That’s because you pay for every square metre you construct, even if some of it doesn’t count toward FAR. The cost per FAR unit figure uses the FAR-counted area instead, since it’s meant to compare the value of usable floor area across schemes.

Worked Example: A 400 m² Plot With a G+3 Building

Say you have a 400 m² plot. Ground footprint is 200 m². Three upper floors, each matching the footprint. No basement. Max FAR is 2.0. Max coverage is 60%. Construction cost is $1,200 per m². Land cost is $400,000.

• Plot area: 400 m²

• Footprint: 200 m²

• Upper floors: 3 × 200 = 600 m²

• Total built-up area: 200 + 600 = 800 m²

• FAR-counted area (no basement): 800 m²

• FAR: 800 ÷ 400 = 2.000

• Coverage: (200 ÷ 400) × 100 = 50.00%

• Permissible area: 2.0 × 400 = 800 m²

• FAR utilisation: (2.0 ÷ 2.0) × 100 = 100.0%

• Remaining allowance: 0 m²

• Compliance: at the FAR limit and under the coverage limit, so compliant

• Construction cost: 800 × $1,200 = $960,000

• Total cost: $960,000 + $400,000 = $1,360,000

• Cost per FAR unit: $1,360,000 ÷ 800 = $1,700 per m²

The scheme sits exactly at the FAR cap, which means any additional floor area would exceed it. The coverage of 50% leaves headroom under the 60% cap, so the ground floor could grow without breaking coverage rules, but FAR would break first. That’s the kind of tension the calculator exists to surface.