FAR & Density
Calculator
Enter a site area and floor area ratio to explore a planning scenario for gross floor area, net area, units, population, parking, and density.
Who it's for: developers, architects, and planners comparing pre-design site-planning scenarios from verified local inputs.
How to use this calculator
The formula
GFA scenario = Site Area × Entered FAR
Net-area scenario = GFA × Net-to-Gross Ratio
Units = floor(Net Area ÷ Average Unit Size)
Population = round(Units × Persons per Unit)
Parking = ceil(Units × Spaces per Unit)
Unit Density = Units ÷ Site Area in hectares
Site Area is the user-entered lot area in m².
Entered FAR is the ratio supplied by the user from a local source.
Net-to-Gross Ratio is the assumed share of GFA available for the program.
Average Unit Size, Persons per Unit, and Spaces per Unit are editable planning assumptions.
The unit count is rounded down, population is rounded to the nearest person, and parking is rounded up.
Worked example
When this estimate will be off
- Assumes a flat, unconstrained envelope — setbacks, height limits, lot coverage maximums, or floodplain overlays can reduce achievable GFA below what the FAR alone permits.
- Net-to-gross ratio is a user-entered programming assumption. Derive it from the project brief, area schedule, comparable design evidence, or an explicit sensitivity range rather than a generic building-type benchmark.
- Average unit size is a blunt input. A real mix of studios, one-bedroom, and two-bedroom units will produce a different total count than a flat average.
- The parking result applies only the entered spaces-per-unit assumption. Local minimums, maximums, reductions, exemptions, and accessible-space rules require separate verification.
Frequently asked questions
A common mistake: Assumes a flat, unconstrained envelope — setbacks, height limits, lot coverage maximums, or floodplain overlays can reduce achievable GFA below what the FAR alone permits.
FAR, or floor area ratio, is gross floor area divided by the site area defined by the applicable zoning instrument. Density expresses units or people per unit of land area. The local rules decide what counts toward floor area and site area, so those definitions must be verified before using the ratio.
Divide gross floor area by site area when both areas follow the same local zoning definitions. A 7,000 m² gross-floor-area scenario on a 2,000 m² site produces a FAR of 3.5. Multiplying site area by an entered FAR reverses the arithmetic, but it does not independently establish permitted floor area.
FAR sets the floor area; density follows from how that area is divided. Multiply site area by FAR, apply a net-to-gross ratio, then divide by average unit size. A 2,000 m² site at FAR 3.5, 80% net, and 85 m² units yields about 65 units, or 325 units per hectare.
No. The calculator applies arithmetic to values supplied by the user. A zoning review must confirm the governing jurisdiction, effective ordinance and map, official lot area, floor-area definition, exclusions, bonuses, overlays, setbacks, height, lot coverage, parking rules, and any discretionary approvals before the result is treated as development capacity.
Sources
- Calculation basis — Arithmetic applied to user-entered site area, FAR, efficiency, unit size, occupancy, and parking assumptions; the calculator does not supply zoning entitlements.
- Required local authority — Verify the effective zoning instrument, official parcel area, floor-area definitions, overlays, bonuses, dimensional controls, and parking rules for the selected site.
This free FAR / Density Calculator is built and maintained by DataDrivenAEC, using the relevant codes and standards. It does not substitute for professional judgment.