Per Square Foot Per Plot Ratio: How to Calculate It

“Per square foot per plot ratio” usually refers to floor area ratio (FAR), also called plot ratio: the total floor area of a building divided by the area of its land parcel. Enter the building’s total floor area and the plot area to calculate the ratio; the result is dimensionless, such as 2.0, meaning two square feet of floor area per square foot of land.

Formula

Floor area ratio (FAR) = total floor area ÷ plot area. In symbols, FAR = F ÷ P, where F is the counted floor area of the building, measured in square feet (ft²) or square metres (m²), and P is the area of the plot, measured in the same area unit. Because the units divide out, the ratio has no physical unit: ft²/ft² and m²/m² both reduce to a plain number. The calculator displays the equivalent unit labels to make clear which areas are being compared.

The calculation treats total floor area as an input. It does not decide which spaces local planning rules include or exclude. For a regulatory calculation, use the authority’s definition of floor area and plot area, not an assumed measurement convention.

Worked Example

Using the calculator’s defaults:

1. Total floor area, F = 20,000 ft².
2. Plot area, P = 10,000 ft².
3. Divide: 20,000 ÷ 10,000 = 2.

The result is a floor area ratio of 2.00, or 2.00 square feet of counted floor area per square foot of plot. In metric terms, the same ratio is 2.00 m²/m². For instance, if both areas are converted to square metres before dividing, the conversion factor cancels and the answer remains 2.00.

What the Ratio Means

FAR compares the size of a building’s floor area with the land beneath it. A ratio of 1.0 means counted floor area equals plot area; 2.0 means it is twice the plot area; and 0.5 means it is half the plot area. It is a measure of development intensity, not a direct description of a building’s height, footprint, or number of units.

For example, a 10,000 ft² plot with a 20,000 ft² building has FAR 2.0. One possible design could have two floors of 10,000 ft² each. Another might have four floors of 5,000 ft² each. Both have the same ratio, even though their footprints and heights differ. Actual buildings may have still more complex shapes, and site rules can constrain what is feasible.

“Per square foot” in this phrase describes the relationship between two areas. It does not mean a price per square foot, a construction cost, or the area of an individual room. The ratio itself is not measured in dollars or in square feet.

How to Measure the Inputs

Use the area of the entire plot for P and the relevant total floor area for F. If a property has multiple buildings or floors, add the areas that the chosen definition counts. A floor’s area is not automatically the same as the building’s ground-level footprint: upper floors may extend beyond it, or occupy only part of it.

• Keep units consistent. Do not divide square feet by square metres. Convert one area first, or use the same unit for both inputs.
• Use area units, not length units. A plot measuring 100 ft by 100 ft has an area of 10,000 ft², not 200 ft.
• Check what “floor area” includes. Definitions can treat basements, parking, balconies, mechanical areas, and other spaces differently.
• Check the plot boundary. The relevant land area may depend on the parcel or planning definition, including how shared or excluded land is handled.

If a parcel has an irregular shape, use a reliable surveyed area or calculate its component shapes and add them. Do not estimate a complicated boundary from a rough sketch if the result will be used for a planning application or purchase decision.

Using FAR to Compare Design Scenarios

The calculator is useful for quick comparisons. If a design has 30,000 ft² of counted floor area on a 15,000 ft² plot, its FAR is 2.0. If the same plot instead has 24,000 ft² of counted area, the FAR is 1.6. This makes it easy to compare proposals without confusing total floor space with land size.

FAR can also be rearranged for preliminary arithmetic:

• Estimated counted floor area = FAR × plot area.
• Plot area = total floor area ÷ FAR.

For example, a hypothetical target ratio of 1.5 on a 10,000 ft² plot corresponds arithmetically to 15,000 ft² of floor area. This is only a mathematical illustration, not confirmation that the area is permitted or can be built. Height limits, setbacks, lot coverage, access, parking, design requirements, and other controls may independently affect a proposal.

Common Misunderstandings and Limits

A frequent misconception is that FAR alone tells you how tall a building can be. It does not. A low-rise building covering most of a site and a taller building with a smaller footprint can have the same FAR. The ratio also does not reveal how much open space remains at ground level, how rooms are arranged, or how many dwellings fit inside.

Another common source of error is using a gross floor area from one source and a net or otherwise differently defined floor area from another. Those figures may not be comparable. Planning authorities and property documents can define the numerator and denominator in specific ways; exemptions and exclusions should not be guessed. The calculator reports only the arithmetic result from the numbers entered.

Rounding matters when results are close to a threshold. The display rounds to two decimal places, so retain the unrounded values for checks where precision matters. A displayed 1.50 could represent a slightly lower or higher underlying value. Confirm exact figures and applicable rules with the relevant planning authority or a qualified local professional before relying on a compliance conclusion.

Frequently Asked Questions

Is FAR the same as plot ratio?
In many planning contexts, “floor area ratio” and “plot ratio” refer to the same basic comparison: counted floor area divided by plot area. The exact terms and measurement rules vary by place, so check the local definition.

Can FAR have units?
No. When both areas use the same unit, the units cancel. A result of 2.0 can be described as 2 square feet of floor area per square foot of plot, but the ratio itself is dimensionless.

Does a FAR of 2 mean two floors?
No. It means the counted floor area is twice the plot area. The area could be distributed across different numbers of floors and footprints, subject to other design and planning constraints.

Should I include basements or parking areas?
It depends on the applicable floor-area definition. Some rules may count particular basement, parking, or service spaces differently or exclude them. Use the local authority’s stated method rather than assuming they all count.

How do I calculate FAR from square metres?
Divide total counted floor area in square metres by plot area in square metres. If both figures are in square metres, the result is directly comparable with a calculation made in square feet.

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in f | Total floor area | ft² | 20000 | 0 | 100000000
in p | Plot area | ft² | 10000 | 0.01 | 100000000
out r | Floor area ratio | ft²/ft² | f / p | 2
out m | Floor area per plot area | m²/m² | f / p | 2