Floor Area Ratio Calculator | FAR Calculator Tool

Floor Area Ratio (FAR) Calculator

Floor area ratio (FAR) is a number that compares the total floor space inside a building to the size of the land it sits on. Planners and architects use it to control how much building a plot of land is allowed to hold. This calculator finds FAR by dividing total building area by plot area.

What is floor area ratio?

FAR is one of the main tools cities use to control building density, meaning how much construction is packed onto a piece of land. A city sets a maximum FAR for each zone. A low FAR allows only small, spread-out buildings. A high FAR allows tall or bulky buildings that use most of the site's potential.

FAR goes by other names in different countries. India calls it floor space index (FSI). The United Kingdom and Hong Kong call it plot ratio. Parts of Europe call it site intensity. The underlying idea is the same everywhere.

Floor area ratio formula

FAR is total building area divided by plot area:

$FAR = \frac{\text{Total Building Area}}{\text{Plot Area}}$

• Total building area is the sum of the floor area on every level of the building.
• Plot area is the size of the land parcel the building stands on.

Both values must use the same unit, either square feet or square meters. The result is a plain number, not a percentage. A FAR of 1.0 means the building's total floor space equals the size of the plot. A FAR of 3.0 means the total floor space is three times the plot size, which usually means a multi-story building.

Local rules vary on what counts as building area. Some cities exclude basements, parking garages, or mechanical rooms. Others count balconies at a reduced rate. Anyone doing a real permit application should check the local zoning code for the exact definition.

How to calculate floor area ratio

1. Add up the floor area of every level of the building to get total building area.
2. Measure the area of the land plot.
3. Make sure both numbers use the same unit.
4. Divide total building area by plot area.

Example

A building has 5 floors. Each floor covers 10,000 square feet, so the total building area is 50,000 square feet. The plot beneath it measures 20,000 square feet.

$FAR = \frac{50{,}000}{20{,}000} = 2.5$

The building's floor space is two and a half times the size of its plot. That result, 2.5, is the FAR.

A second example: a single-story shop with 5,000 square feet of floor space sits on a 10,000-square-foot lot.

$FAR = \frac{5{,}000}{10{,}000} = 0.5$

A FAR of 0.5 means the building uses only half as much floor space as the lot could support under a FAR of 1.0.

Typical FAR ranges by zone

These ranges are only examples. Exact limits are set by each city or county and can differ sharply from one neighborhood to the next.

Why FAR matters

Zoning compliance. Cities cap FAR to limit how much can be built on a lot. A project must stay under the local maximum, or it needs a variance or special permit.

Development potential. A property that uses less than its allowed FAR has room to expand. Investors look for this unused capacity because it can be built out later or, in some cities, sold to another site through a transfer-of-development-rights program.

Urban planning. Setting different FAR limits by neighborhood lets a city put dense construction downtown while keeping outlying areas low-rise. It also affects how much traffic, water use, and sewage a neighborhood must support, since more floor space usually means more people.

Renovation and expansion. An older building might already sit above the FAR a newer zoning code allows. In that case, additions may be restricted even if the lot looks like it has open space.

Related measures

FAR is not the only way to measure density. Lot coverage measures the share of a lot covered by the building's footprint at ground level, ignoring height. A tall, narrow tower can have a high FAR but low lot coverage. Height limits cap a building's vertical size directly. Setback rules require empty space between a building and the property line. Cities often combine several of these rules rather than relying on FAR alone.

History

New York City adopted one of the first modern zoning codes in 1916, which controlled building bulk through setback and height rules rather than a single ratio. New York's 1961 zoning revision introduced FAR directly as a citywide density control, and other cities later adopted similar systems. Since then, many places have added bonus provisions that let developers exceed the base FAR in exchange for public benefits, such as plazas or affordable housing units.

Frequently asked questions

What is a good floor area ratio? There is no universal "good" FAR. It depends entirely on the zone. A FAR of 0.5 is normal for a low-density suburb, while a FAR of 10 or higher is common in a dense city center.

Can floor area ratio be greater than 1? Yes. A FAR above 1.0 just means the total floor space across all levels is larger than the plot itself, which happens whenever a building has more than one story covering most of the lot.

Does FAR include basements and parking? It depends on local rules. Many zoning codes exclude basements, underground parking, and mechanical rooms from the FAR calculation, but this varies by city, so the local code should always be checked.

How is FAR different from lot coverage? FAR counts total floor area across every level of a building. Lot coverage counts only the building's footprint on the ground. A 10-story building on a small footprint can have a high FAR and low lot coverage at the same time.

How do I find the maximum FAR allowed on my property? Check the local zoning map and zoning code, usually published by a city or county planning department, or ask a local architect or planning office directly.

References

1. New York City Department of City Planning. "Glossary of Planning Terms."
2. Talen, E. (2012). City Rules: How Regulations Affect Urban Form. Island Press.
3. Pont, M. B., & Haupt, P. (2010). Spacematrix: Space, Density and Urban Form. NAi Publishers.