Free tool · no sign-up
FSI & site coverage calculator
Estimate what a site's zoning permits on paper: the maximum gross floor area at a floor space index (FSI, called FAR in the US), the largest footprint at a site-coverage limit, and the coverage and density of a proposed or existing building. Areas in square feet, square metres, acres or hectares; nothing leaves your browser.
Results
- Site area
- 217,800 sq ft20,234.3 m²
- Maximum gross floor area
- 108,900 sq ft10,117.1 m²
- Maximum footprint
- 108,900 sq ft10,117.1 m²
- Coverage of the building
- 43.6%
- Gross floor area of the building
- 95,000 sq ft8,825.8 m²
- FSI achieved
- 0.44×
- Storeys needed to reach the maximum
- 1.15
Arithmetic only: the zoning by-law's definitions, setbacks, height and parking rules decide what can be built. Calculated in your browser; nothing is sent or saved.
How it’s calculated
- Maximum gross floor area
Max GFA = site area × FSI (FAR) - Maximum footprint
Max footprint = site area × coverage limit ÷ 100 - Coverage achieved
Coverage = building footprint ÷ site area × 100 - Density achieved
FSI achieved = gross floor area ÷ site area
Worked example (illustrative numbers)
- A 5.00-acre industrial site is 217,800 sq ft (20,234.3 m²).
- At a maximum FSI of 0.5, the zoning permits up to 108,900 sq ft (10,117.1 m²) of gross floor area. With a 50% coverage limit, the largest footprint is also 108,900 sq ft.
- A proposed single-storey building with a 95,000 sq ft footprint covers 43.6% of the site and reaches an FSI of about 0.44.
- On an urban site of 4,000 m² (43,056 sq ft), an FSI of 3.0 permits about 12,000 m² (129,167 sq ft) of gross floor area.
Illustrative figures only; they are not the zoning permissions of any property or municipality.
FSI, FAR and coverage in plain terms
Floor space index (FSI) is the ratio of a building's gross floor area to the area of its lot. Many Ontario by-laws use FSI; other Canadian municipalities say floor area ratio (FAR) or density, and US zoning codes almost always say FAR. An FSI of 2.0 on a 10,000 sq ft lot permits up to 20,000 sq ft of floor area, whether as two storeys over the whole lot or four storeys over half of it.
Site coverage (lot coverage) limits the share of the lot the building's footprint may occupy. Coverage and FSI work together: a low coverage limit with a high FSI pushes a building up; a high coverage limit with a low FSI suits single-storey industrial and retail.
Read the definitions in the by-law
The arithmetic is simple; the definitions are not. By-laws differ on what counts as gross floor area (basements, mezzanines, parking structures, mechanical rooms and stairwells are often excluded or partly counted), on whether the lot area is measured before or after road widenings and conveyances, and on how coverage treats canopies, decks and accessory buildings. Some zones set density in units per hectare instead of FSI. Use the definitions in the governing by-law, and note any site-specific exception or minor variance.
Other rules often limit a site before FSI does: setbacks, height limits, angular planes, parking and loading requirements, landscaping minimums, stormwater management, easements and environmental setbacks. Treat the maximum from this calculator as an upper bound, not a buildable program.
Presenting density in a land brochure
Buyers of development land price the permission, so state the zone, the by-law and the controls as written: "Maximum FSI 0.5; maximum lot coverage 50% (By-law <number>-<year>)". If you also show a buildable area, say how it was calculated and that it is before setbacks, parking and approvals. A concept plan prepared by a planner or architect carries more weight than a formula, and should be labelled with its date and status.
In OfferingStack the zoning page shows the zone, the permitted uses and the zoning controls you enter as printed in the by-law, with the source; values found by research are shown only after you accept them.
Estimates for marketing and screening only. This is not an appraisal, a planning opinion, or legal advice; the zoning by-law and the municipality govern what can be built.
Questions
How do you calculate FSI?
Divide the building's gross floor area by the lot area, using the same units. 95,000 sq ft of floor area on a 217,800 sq ft (5-acre) lot is an FSI of about 0.44.
Is FSI the same as FAR?
Yes, they describe the same ratio of floor area to lot area. Ontario by-laws often say FSI; US zoning codes and some Canadian municipalities say FAR. The by-law's own definition of gross floor area decides what is counted.
What is the difference between FSI and lot coverage?
FSI limits total floor area across all storeys; lot coverage limits the share of the lot the building footprint may cover. A building must satisfy both, along with setbacks, height and parking rules.
Where do I find a property's FSI?
In the municipality's zoning by-law for the property's zone, including any site-specific exceptions, and sometimes in the official plan. This calculator doesn't look up zoning; it only does the arithmetic on the figures you enter.
Is my data saved?
No. The calculation runs in your browser and nothing you type is sent to OfferingStack.
Related
Put the numbers in a finished offering memorandum.
Upload your fact sheet or rent roll, add the NOI and price, and review a watermarked preview of the financial and pricing pages before you buy anything.