Understanding how much floor area can be developed on a parcel of land is an important part of property planning, zoning analysis, architecture, and real estate development. The Floor Area Ratio (FAR) is one of the most commonly used measurements for comparing a building's total floor area with the size of the lot on which it sits.

Our Floor Area Ratio Calculator makes this calculation simple. Enter the gross floor area and lot area to calculate FAR instantly. If you already know the permitted FAR, you can use the second calculator to determine the maximum floor area allowed by that ratio. The third calculator helps compare existing and proposed floor area with a permitted FAR limit to estimate remaining development capacity.

Important: FAR regulations and the definition of floor area vary between cities and jurisdictions. These calculators perform the mathematical calculations using the values you provide. They do not determine whether a specific property is legally buildable or whether a project satisfies every local zoning requirement.

What Is Floor Area Ratio?

Floor Area Ratio (FAR) is the relationship between the total floor area of a building and the area of the lot or site on which the building is located.

It is calculated by dividing the gross floor area by the lot area.

\(FAR = \frac{Gross\ Floor\ Area}{Lot\ Area}\)

For example, if a building has 20,000 square feet of gross floor area on a 10,000-square-foot lot:

\(FAR = \frac{20,000}{10,000} = 2.0\)

The FAR is therefore 2.0.

A FAR of 2.0 means the building's total floor area is equal to 200% of the lot area. It does not necessarily mean that the building has two floors. The same total floor area could be distributed across different numbers of stories and different building footprints.

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How to Use the Floor Area Ratio Calculator

The primary calculator requires two area measurements:

1. Gross Floor Area
2. Lot or Site Area

You also select the area unit used for your measurements.

Step 1: Enter the Gross Floor Area

Enter the total floor area that is being considered for the FAR calculation.

For example:

25,000 ft²

Step 2: Enter the Lot Area

Enter the total area of the parcel or site.

For example:

10,000 ft²

Step 3: Select the Area Unit

The calculator supports common area units. Because FAR is a ratio of two areas, the two measurements must use the same unit.

For example, you can use:

• square feet
• square meters
• square yards
• acres
• hectares

Step 4: Calculate FAR

The calculator divides gross floor area by lot area and returns the resulting FAR.

For a 25,000 ft² building on a 10,000 ft² lot:

\(FAR = \frac{25,000}{10,000} = 2.5\)

The resulting FAR is 2.5.

Floor Area Ratio Formula

The basic FAR formula is:

\(FAR = \frac{GFA}{A_L}\)

Where:

• FAR = Floor Area Ratio
• GFA = Gross Floor Area
• Aₗ = Lot or Site Area

Because both values represent areas, they must be expressed in compatible units.

For example, you should not divide 20,000 square feet by 1 acre without first converting the units.

FAR Calculation Example

Suppose a commercial building has:

• Gross floor area = 36,000 ft²
• Lot area = 12,000 ft²

Using the FAR formula:

\(FAR = \frac{36,000}{12,000}\)

\(FAR = 3.0\)

The property has an FAR of 3.0.

This means the gross floor area is three times the area of the lot.

What Does a FAR of 1 Mean?

A FAR of 1.0 means the total floor area equals the lot area.

For example:

• Lot area = 10,000 ft²
• Gross floor area = 10,000 ft²

\(FAR = \frac{10,000}{10,000}=1.0\)

However, FAR does not tell you how the building is distributed vertically.

A 10,000 ft² building could theoretically be arranged as:

• one 10,000 ft² floor;
• two 5,000 ft² floors;
• four 2,500 ft² floors; or
• another combination producing the same total floor area.

Actual development would depend on local requirements such as setbacks, height restrictions, lot coverage, parking, open-space requirements, and other zoning regulations.

What Does a FAR of 2 Mean?

A FAR of 2.0 means the total floor area is twice the lot area.

For a 10,000 ft² lot:

\(GFA = 10,000 \times 2 = 20,000\ ft^2\)

The allowable or calculated floor area would therefore be 20,000 ft² if 2.0 is the applicable FAR limit and all of that floor area is counted under the relevant zoning rules.

A FAR of 2 does not automatically mean a two-story building.

For example:

Building arrangement	Total floor area	Lot area	FAR
1 × 10,000 ft² floor	10,000 ft²	10,000 ft²	1.0
2 × 10,000 ft² floors	20,000 ft²	10,000 ft²	2.0
4 × 5,000 ft² floors	20,000 ft²	10,000 ft²	2.0
5 × 4,000 ft² floors	20,000 ft²	10,000 ft²	2.0

This is why FAR and building height are related but different measurements.

FAR as a Percentage

FAR can also be expressed as a percentage by multiplying the ratio by 100.

\(FAR\ Percentage = FAR \times 100\)

For example:

\(2.5 \times 100 = 250%\)

Therefore, a FAR of 2.5 corresponds to 250% of the lot area in total floor area.

The ratio form, such as 2.5, is the more common way FAR is stated in zoning regulations.

Why Is Floor Area Ratio Important?

FAR provides a standardized way to describe the intensity of development on a site.

It can help planners, architects, developers, property owners, and real estate professionals understand how much floor area a particular parcel can potentially support under a specified FAR limit.

For example, two properties may have the same lot size but different permitted FAR values.

Property A

• Lot = 10,000 ft²
• FAR = 1.0

Potential maximum floor area based only on FAR:

\(10,000 \times 1.0 = 10,000\ ft^2\)

Property B

• Lot = 10,000 ft²
• FAR = 3.0

Potential maximum floor area:

\(10,000 \times 3.0 = 30,000\ ft^2\)

The second property has three times the floor-area capacity based on the stated FAR.

FAR vs. Lot Coverage

FAR and lot coverage are sometimes confused because both describe development intensity, but they measure different things.

FAR compares total floor area with lot area.

\(FAR = \frac{Total\ Floor\ Area}{Lot\ Area}\)

Lot coverage generally compares the building footprint with the lot area.

\(Lot\ Coverage = \frac{Building\ Footprint}{Lot\ Area}\times100\)

Consider a 10,000 ft² lot with a 5,000 ft² building footprint and two floors of 5,000 ft² each.

The lot coverage is:

\(Lot\ Coverage = \frac{5,000}{10,000}\times100 = 50%\)

The FAR is:

\(FAR = \frac{10,000}{10,000}=1.0\)

So the property can have 50% lot coverage and an FAR of 1.0.

This distinction becomes particularly important when planning multi-story buildings.

Maximum Buildable Floor Area From FAR

Sometimes you already know the permitted FAR and want to determine how much floor area that FAR allows.

This is the reverse of the basic FAR calculation.

The formula is:

\(Maximum\ Floor\ Area = Lot\ Area \times Permitted\ FAR\)

For example, suppose:

• Lot area = 15,000 ft²
• Permitted FAR = 2.5

Then:

\(Maximum\ Floor\ Area = 15,000\times2.5\)

\(Maximum\ Floor\ Area = 37,500\ ft^2\)

Based purely on the stated FAR, the maximum floor area is 37,500 ft².

Use the second calculator above when your starting point is the lot size and permitted FAR, rather than an existing building's floor area.

How to Calculate Maximum Buildable Area

Follow these steps:

1. Determine the lot area

Suppose your parcel measures:

8,000 ft²

2. Find the permitted FAR

Suppose the applicable FAR is:

1.75

3. Multiply the two values

\(Maximum\ Floor\ Area = 8,000\times1.75\)

\(Maximum\ Floor\ Area = 14,000\ ft^2\)

Therefore, the FAR calculation produces a maximum floor area of 14,000 ft².

Remember that this is a mathematical result. Actual zoning approval may impose additional restrictions.

How Many Floors Can You Build With a Given FAR?

FAR does not directly determine the number of floors.

However, if you know the planned floor plate or building footprint and assume each floor has the same floor area, you can estimate the number of floors needed to produce a particular total floor area.

The basic relationship is:

\(Number\ of\ Floors = \frac{Total\ Floor\ Area}{Floor\ Area\ per\ Floor}\)

For example:

• Lot area = 10,000 ft²
• FAR = 2.0
• Maximum floor area = 20,000 ft²
• Floor plate = 5,000 ft²

Then:

\(Number\ of\ Floors = \frac{20,000}{5,000}=4\)

A four-floor arrangement with 5,000 ft² per floor would produce 20,000 ft² of total floor area.

But FAR alone does not establish that four floors are legally permitted. Height limits, setbacks, lot coverage, floor-to-floor height, and other rules may affect the actual design.

Required Lot Area for a Desired Floor Area

Another useful reverse calculation is finding the lot area required for a desired amount of floor area.

Rearranging the FAR formula:

\(FAR = \frac{GFA}{Lot\ Area}\)

gives:

\(Lot\ Area = \frac{GFA}{FAR}\)

For example, suppose you want:

30,000 ft² of floor area

and the permitted FAR is:

2.5

Then:

\(Lot\ Area = \frac{30,000}{2.5}=12,000\ ft^2\)

So a 12,000 ft² lot would be required to produce 30,000 ft² at an FAR of 2.5, based purely on the FAR relationship.

Required FAR for a Proposed Building

You can also reverse the calculation to determine what FAR a proposed building would require.

The formula remains:

\(Required\ FAR = \frac{Proposed\ Floor\ Area}{Lot\ Area}\)

Suppose:

• Proposed floor area = 28,000 ft²
• Lot area = 14,000 ft²

Then:

\(Required\ FAR = \frac{28,000}{14,000}=2.0\)

The proposed development requires an FAR of 2.0.

You can then compare that value with the applicable zoning limit.

FAR and Gross Floor Area

The terms FAR and Gross Floor Area (GFA) describe different things.

GFA is an area measurement.

FAR is a ratio.

For example:

• GFA = 25,000 ft²
• Lot area = 10,000 ft²
• FAR = 2.5

The GFA tells you how much floor area exists or is proposed.

The FAR tells you how that floor area compares with the lot size.

The two should therefore not be treated as interchangeable.

What Counts Toward FAR?

This is one of the most important issues when applying FAR to a real property.

The mathematical formula is straightforward, but the legal or zoning definition of floor area is not necessarily universal.

Depending on the jurisdiction, certain areas may be included, partially included, or excluded from the calculation.

Potentially relevant areas may include:

• residential floor area;
• commercial floor area;
• office space;
• enclosed building areas;
• certain parking areas;
• basements;
• mechanical spaces;
• storage areas;
• balconies;
• stairways;
• elevators; and
• other accessory or service areas.

However, the exact treatment varies considerably between zoning codes.

For that reason, do not assume that the architectural gross floor area shown on a plan is automatically identical to the FAR-counted floor area used by the local zoning authority.

Always check the applicable zoning ordinance or development regulations.

What May Be Excluded From FAR?

Some jurisdictions exclude certain areas from FAR calculations or apply special rules to them.

Examples may include particular:

• parking areas;
• mechanical rooms;
• stairwells;
• elevator shafts;
• basements;
• utility areas;
• covered outdoor areas; or
• accessory spaces.

But these exclusions are jurisdiction-specific.

An area that is excluded in one city may be counted in another.

Therefore, the calculator should be used with the floor-area figure that is actually applicable to the relevant zoning regulation.

How to Check FAR Compliance

If you know the permitted FAR and want to determine whether an existing or proposed development stays within that limit, you need to compare the proposed floor area with the maximum floor area allowed by the FAR.

First calculate the maximum floor area:

\(Maximum\ Floor\ Area = Lot\ Area\times Permitted\ FAR\)

Then calculate the proposed total floor area:

\(Proposed\ Total\ Floor\ Area = Existing\ Floor\ Area + Additional\ Proposed\ Floor\ Area\)

Finally:

\(Proposed\ FAR = \frac{Proposed\ Total\ Floor\ Area}{Lot\ Area}\)

If the proposed FAR is less than or equal to the permitted FAR, the proposed floor area is within the entered FAR limit.

FAR Compliance Example

Suppose:

• Lot area = 10,000 ft²
• Permitted FAR = 2.0
• Existing floor area = 12,000 ft²
• Proposed additional floor area = 5,000 ft²

First calculate the maximum floor area:

\(Maximum\ Floor\ Area = 10,000\times2.0=20,000\ ft^2\)

The proposed total floor area is:

\(12,000+5,000=17,000\ ft^2\)

Now calculate proposed FAR:

\(Proposed\ FAR = \frac{17,000}{10,000}=1.7\)

The proposed FAR is 1.7, compared with a permitted FAR of 2.0.

Therefore, the proposed floor area is within the entered FAR limit.

How Much FAR Is Remaining?

You can calculate remaining FAR by subtracting the proposed FAR from the permitted FAR.

\(Remaining\ FAR = Permitted\ FAR - Proposed\ FAR\)

Using the previous example:

\(Remaining\ FAR = 2.0-1.7=0.3\)

The remaining FAR is therefore 0.3.

You can also convert that remaining FAR into remaining floor area:

\(Remaining\ Floor\ Area = Maximum\ Floor\ Area - Proposed\ Total\ Floor\ Area\)

\(Remaining\ Floor\ Area = 20,000-17,000=3,000\ ft^2\)

So the development has 3,000 ft² of remaining floor-area capacity based on the entered FAR limit.

What Does FAR Used Percentage Mean?

The FAR used percentage shows how much of the permitted FAR has already been consumed.

It can be calculated as:

\(FAR\ Used\ % = \frac{Proposed\ FAR}{Permitted\ FAR}\times100\)

For the previous example:

\(FAR\ Used\ % = \frac{1.7}{2.0}\times100=85%\)

Therefore, the proposed development uses 85% of the permitted FAR.

This can be useful when evaluating whether additional floor area might remain available.

What Happens If the Proposed FAR Exceeds the Limit?

Suppose:

• Lot area = 10,000 ft²
• Permitted FAR = 2.0
• Proposed floor area = 23,000 ft²

The proposed FAR would be:

\(Proposed\ FAR = \frac{23,000}{10,000}=2.3\)

Since:

\(2.3 > 2.0\)

the proposed floor area exceeds the entered FAR limit.

The amount above the maximum floor area is:

\(23,000-20,000=3,000\ ft^2\)

So the proposal exceeds the FAR-based maximum by 3,000 ft², assuming all 23,000 ft² is counted toward FAR.

The third calculator identifies this condition automatically.

FAR vs. Building Height

FAR and building height are separate zoning concepts.

A property could have a relatively high FAR but a low lot coverage requirement, potentially resulting in a multi-story building.

Conversely, a property could have a lower FAR but allow a larger building footprint.

For example, consider a 10,000 ft² lot with FAR 2.0.

The total floor area associated with that FAR is:

\(10,000\times2.0=20,000\ ft^2\)

That 20,000 ft² could theoretically be distributed in many ways:

• 2 floors × 10,000 ft²
• 4 floors × 5,000 ft²
• 5 floors × 4,000 ft²
• 10 floors × 2,000 ft²

The actual permitted arrangement depends on other development regulations.

FAR vs. FSI

Floor Space Index (FSI) is another term used for a ratio comparing floor area with site area.

In many contexts, FSI and FAR describe essentially the same mathematical relationship:

\(FSI = \frac{Total\ Floor\ Area}{Site\ Area}\)

and:

\(FAR = \frac{Total\ Floor\ Area}{Lot\ Area}\)

However, terminology and regulatory definitions can vary by country and jurisdiction.

In the United States, Floor Area Ratio (FAR) is the more commonly encountered terminology in zoning contexts.

FAR vs. Floor Space Ratio (FSR)

Floor Space Ratio (FSR) is another term that may be used for a similar concept.

The basic relationship is:

\(FSR = \frac{Floor\ Space}{Site\ Area}\)

Depending on the jurisdiction, FSR, FAR, plot ratio, and FSI may be used interchangeably or may have specific regulatory definitions.

Therefore, when working on an actual development project, use the terminology and definition provided by the applicable local zoning code.

FAR vs. Plot Ratio

Plot ratio is also commonly used to describe the relationship between building floor area and site area.

A simplified mathematical representation is:

\(Plot\ Ratio = \frac{Total\ Floor\ Area}{Plot\ Area}\)

The terminology is particularly common in some countries outside the United States.

For U.S. zoning research, however, FAR is generally the most useful search term.

FAR and Lot Size: Quick Reference Examples

The following examples illustrate how the same FAR behaves with different lot sizes.

Lot Area	FAR	Floor Area
5,000 ft²	1.0	5,000 ft²
5,000 ft²	2.0	10,000 ft²
10,000 ft²	1.5	15,000 ft²
10,000 ft²	2.0	20,000 ft²
10,000 ft²	2.5	25,000 ft²
20,000 ft²	2.0	40,000 ft²
20,000 ft²	3.0	60,000 ft²

The relationship is always:

\(Floor\ Area = Lot\ Area\times FAR\)

when calculating the floor-area amount associated with a specified FAR.

Common FAR Calculation Mistakes

1. Mixing area units

Do not calculate FAR using different units.

For example, don't divide square feet by square meters without conversion.

Both values should be expressed in the same unit.

2. Confusing FAR with lot coverage

FAR measures total floor area.

Lot coverage measures building footprint relative to lot area.

They are not the same calculation.

3. Assuming FAR equals number of floors

An FAR of 3 does not automatically mean a three-story building.

The number of floors depends on the amount of floor area placed on each level and other zoning restrictions.

4. Assuming all gross building area counts toward FAR

Local zoning regulations may define FAR-counted floor area differently from architectural gross floor area.

Always verify applicable exclusions and definitions.

5. Assuming FAR is the only development restriction

A property can satisfy its FAR limit and still be restricted by:

• setbacks;
• lot coverage;
• building height;
• parking requirements;
• open-space requirements;
• density limits;
• frontage requirements;
• landscaping standards;
• fire and building codes; or
• other local regulations.

FAR is therefore one development metric, not a complete zoning approval test.

Frequently Asked Questions

What is the formula for FAR?

The basic formula is:

\(FAR = \frac{Gross\ Floor\ Area}{Lot\ Area}\)

Divide the applicable gross floor area by the lot or site area.

How do I calculate FAR from square feet?

Divide the building's applicable floor area in square feet by the lot area in square feet.

For example:

\(FAR = \frac{20,000\ ft^2}{10,000\ ft^2}=2.0\)

How much can I build on a 10,000 square foot lot?

It depends on the permitted FAR.

For example, at FAR 2.0:

\(10,000\times2.0=20,000\ ft^2\)

So the FAR-based floor-area amount would be 20,000 ft².

Other zoning restrictions may reduce the actual development potential.

What does a FAR of 2.5 mean?

A FAR of 2.5 means the total floor area is 2.5 times the lot area.

For a 10,000 ft² lot:

\(10,000\times2.5=25,000\ ft^2\)

Can FAR be greater than 1?

Yes.

FAR can be greater than 1 when the total floor area exceeds the area of the lot.

For example:

\(FAR = \frac{30,000}{10,000}=3.0\)

A FAR of 3.0 means the floor area is three times the lot area.

Is FAR the same as lot coverage?

No.

FAR considers total floor area across all floors, while lot coverage generally considers the building footprint relative to the lot.

Does FAR determine building height?

No.

FAR controls or describes the relationship between total floor area and site area. Building height is generally governed separately.

Can I calculate maximum buildable area from FAR?

Yes.

Use:

\(Maximum\ Floor\ Area = Lot\ Area\times Permitted\ FAR\)

Our second calculator is designed specifically for this calculation.

How do I calculate remaining FAR?

Subtract the proposed FAR from the permitted FAR:

\(Remaining\ FAR = Permitted\ FAR - Proposed\ FAR\)

If the result is positive, there is remaining FAR based on the values entered.

How do I calculate remaining buildable floor area?

First calculate maximum floor area:

\(Maximum\ Floor\ Area = Lot\ Area\times Permitted\ FAR\)

Then subtract proposed total floor area:

\(Remaining\ Floor\ Area = Maximum\ Floor\ Area-Proposed\ Total\ Floor\ Area\)

Is FAR the same in every U.S. city?

No.

FAR limits and the definitions used to calculate floor area are determined by local zoning regulations and can vary substantially between jurisdictions.

Always consult the applicable zoning code or planning authority for a property-specific determination.

Final Takeaway

Floor Area Ratio is a straightforward mathematical ratio, but applying it to an actual development project requires understanding the local zoning rules that determine both the permitted FAR and the floor area that counts toward that ratio.

The fundamental relationship is:

\(FAR = \frac{Gross\ Floor\ Area}{Lot\ Area}\)

When the permitted FAR is known, you can reverse the calculation:

\(Maximum\ Floor\ Area = Lot\ Area\times FAR\)

And when evaluating an existing or proposed development, you can compare the proposed floor area with the permitted FAR to determine the remaining FAR-based capacity.

Use the first calculator to calculate FAR, the second calculator to estimate maximum floor area from a permitted FAR, and the third calculator to evaluate proposed floor area against a FAR limit.

For actual zoning, permitting, or development decisions, always verify the applicable local regulations because FAR is only one part of the overall development-control system.