To calculate FAR, divide the total floor area of a building by the area of the lot it sits on. A 2,000 square metre building on a 1,000 square metre lot has a floor area ratio of 2.0. The ratio sets how much you may build, not how tall or how wide.
That number decides more about a scheme than almost any other line in a zoning code. It caps the quantity of space you can sell or lease and leaves the shape open, so two architects given the same lot and ratio can produce a four storey block and a slim eight storey tower, both legal. What follows is the arithmetic, the traps in the definition of floor area, and the controls that shape the result.
What Is Floor Area Ratio?
Floor area ratio relates how much floor space a building contains to how much land it occupies. Zoning codes use it as a density control: rather than dictate a form, the code caps quantity and lets the design team place it.
The New York City Zoning Resolution puts it plainly: floor area ratio is "the total floor area on a zoning lot, divided by the lot area of that zoning lot," and where several buildings share a lot you sum their floor areas first. Its worked example gives a 10,000 square foot lot carrying a 20,000 square foot building a ratio of 2.0. The wording sits in Article I, Chapter 2 of the NYC Zoning Resolution.
Because the ratio is dimensionless it travels between metric and imperial systems. What does not travel is the definition of floor area, and that is where most errors begin.
How to Calculate FAR Step by Step
The formula is short. Getting the two inputs right takes longer than the division.
- Confirm the lot area from the survey, using the legal zoning lot boundary and subtracting land dedicated to road widening where required.
- Measure the floor area of every storey that counts, using the local rule for where to measure from, often the exterior face of exterior walls.
- Remove the areas the code exempts, such as cellar space, plant rooms or certain parking levels.
- Add the remaining areas across all storeys and all buildings on the lot, then divide that total by the lot area.
A 1,000 square metre lot at FAR 2.0 permits 2,000 square metres of countable floor area. A 10,000 square foot lot at FAR 0.5 permits 5,000 square feet, covering half the site on one storey. Backwards, if a brief needs 3,600 square metres and the zone allows 1.8, the smallest workable lot is 2,000 square metres.
💡 Pro Tip
Build a FAR budget spreadsheet on day one of concept design, one row per storey, with separate columns for countable and exempt area. Experienced project architects keep the exempt column visible rather than deleting it, because a plan reviewer will ask why a 900 square metre floor plate reports 740, and the answer should sit on the same sheet.
Why the Same FAR Produces Very Different Buildings
FAR is a budget, not a blueprint. Spend it on a wide footprint and you get a low building with little open ground; spend it on a narrow one and the same space climbs into a tower with a garden around it. The table spends FAR 2.0 on a 1,000 square metre lot four ways, at 3.5 metres floor to floor.
Same Ratio, Four Different Massings
| Scheme | Footprint | Lot coverage | Storeys | Approx. height | Open ground |
|---|---|---|---|---|---|
| Low perimeter block | 500 m² | 50% | 4 | 14 m | 500 m² |
| Mid-rise bar | 400 m² | 40% | 5 | 17.5 m | 600 m² |
| Point block | 250 m² | 25% | 8 | 28 m | 750 m² |
| Slender tower | 200 m² | 20% | 10 | 35 m | 800 m² |
Every row is FAR 2.0, yet the street experience differs completely, and so does the structural logic, since a ten storey tower raises stability questions a four storey block never faces. Our explainer on how skyscrapers stay up covers what changes with height, and a massing and diagram set tests options like these at concept stage.
What Counts as Floor Area and What Does Not
The numerator is what gets people into trouble. Gross floor area in a zoning code is a legal quantity, not the number your BIM model reports by default, and codes routinely exclude space that exists but does not count.
New York's definition includes basement space, penthouse floor space, attic space with eight feet or more of structural headroom, and interior balconies and mezzanines. It excludes cellar space unless used for dwelling purposes, elevator and stair bulkheads, uncovered steps, attic space under eight feet of headroom, and accessory mechanical equipment. Parking is treated in layers, by how high above curb level it sits.
Singapore runs the same idea on different wording. The Urban Redevelopment Authority defines gross floor area as "the total area of covered floor space, including the half thickness of external walls or other building facade elements (e.g. windows, railings, curtain walls), but excluding voids," and counts all covered floor area unless it is specifically exempted. The rules sit in the URA's gross floor area handbook.
📐 Technical Note
Measurement convention matters as much as the inclusion list. New York measures from the exterior faces of exterior walls, or the centre lines of walls separating two buildings. Singapore counts half the thickness of the external wall. On a deep plan with 400 mm walls, that difference alone can shift reported area by a percentage point.
⚠️ Common Mistake to Avoid
The most common error is exporting a gross construction area schedule from the model and calling it floor area. The two are rarely equal, since the model counts plant rooms, cellars and covered parking the code may exempt. Rebuild the schedule against the local definition first.
How FAR, Lot Coverage, Height and Setbacks Work Together
FAR almost never acts alone. It forms one wall of a building envelope built from controls that apply at once, and the binding control is whichever runs out first.
- Lot coverage caps the footprint, defined in New York as the portion of the zoning lot covered by a building when viewed directly from above.
- Height limits and storey counts cap the vertical, while front, side and rear setbacks pull the buildable area in from the boundaries.
- Sky exposure planes, daylight rules, parking and loading all take a further bite.
Run all of them before fixing a massing. A site zoned at FAR 3.0 with a 40 percent coverage cap and a four storey height limit tops out at 1.6, and the extra ratio is unusable. That is a normal outcome rather than a drafting error, and catching it early is one reason planning and design roles overlap, as our comparison of the architect and the urban planner shows.
FAR Bonuses and Transfer of Development Rights
Most codes let you exceed the base ratio in exchange for something the city wants: a public plaza, a through block connection, affordable housing, or conservation of a listed building. Singapore's version is capped and explicit, granting bonus gross floor area of up to 10 percent above the Master Plan gross plot ratio for qualifying incentive schemes.
Transfer of development rights works differently. Where a landmark leaves part of its permitted ratio unused, some codes let that quantity be sold and built on a receiving site nearby. The landmark stays low, the receiving building goes higher, and density across the pair holds close to what the plan intended. Few zoning tools do more to make keeping an old building financially rational, which ties it to adaptive reuse economics.
Density set this way carries beyond the property line, since higher ratios concentrate built mass, paved surface and waste heat, which feed the urban heat island effect.
What FAR Is Called in Other Countries
The same ratio appears worldwide under different names, which matters when you read a foreign code or a competition brief. India uses floor space index, the United Kingdom, Hong Kong and Singapore use plot ratio, New South Wales says floor space ratio, Germany has the Geschossflächenzahl and Brazil the coeficiente de aproveitamento. An international naming overview lists them side by side. The arithmetic is identical everywhere; the inclusion rules are not, so never carry an assumption about balconies, cellars or parking from one jurisdiction to another.
Zoning definitions, bonus schemes and exemption lists vary by jurisdiction and change over time. Verify every figure against the current local code and confirm your calculation with the permitting authority.
Frequently Asked Questions About Floor Area Ratio
What Does a FAR of 1.0 Mean?
A FAR of 1.0 means you may build countable floor area equal to the lot size. On a 500 square metre site that is 500 square metres: one storey covering the whole plot, two storeys on half of it, or four storeys on a quarter. Coverage and setback rules usually rule out the first.
Is Floor Area Ratio the Same as Lot Coverage?
No. Lot coverage measures the footprint seen from above, as a percentage of the lot. FAR measures total floor space across all storeys, as a multiple of lot area. A building can have low coverage and high FAR, which is what a tower on a landscaped podium looks like.
Does a Basement Count Toward FAR?
It depends on the code and the use. New York excludes cellar space unless it is used for dwelling purposes, while basement space is generally included. Other jurisdictions draw the line at how far the floor sits below grade.
How Do I Find the FAR Allowed on a Specific Site?
Identify the zoning district from the municipal zoning map, then read the bulk or density regulations for that district. The permitted ratio often varies by use, so a mixed use scheme may face different caps on its residential and commercial parts.
Putting It All Together
Your Next Step: Before sketching a massing, pull the district's FAR, lot coverage, height and setback figures onto one page and work out the maximum ratio each control allows. The lowest number is your real budget, and designing to it saves redrawing a scheme that was never buildable.
Sources
- Zoning Resolution, Article I Chapter 2 (NYC Department of City Planning)
- Gross Floor Area Handbook (Urban Redevelopment Authority, Singapore)
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