Construction · zoning arithmetic

Lot coverage & floor area ratio calculator.

Enter your lot area and the FAR and coverage limits from your local code, then your existing and proposed areas. See where you stand and how much room is left.

FAR = gross floor area ÷ lot area. Lot coverage = building footprint ÷ lot area. Allowable floor area = lot area × FAR limit.

Any jurisdiction Runs in your browser No zoning database

Inputs

Lot and local limits

Area unit Use the same unit for every area below.

Lot area (sq ft)

FAR limit From your local code. Leave blank to skip.

Lot coverage limit (%) From your local code. Leave blank to skip.

Floor area by level (sq ft)

ExistingProposed (added)

Level 1

Level 2

Level 3

Level 4

Count only the floor area your local code counts (some codes exclude basements, garages, attics or stairwells).

Building footprint (sq ft)

Existing footprint

Proposed added footprint

Include whatever your code counts toward coverage (some include garages, porches or decks).

Your lot

Enter your details and press Calculate.

The formulas

FAR = total gross floor area ÷ lot area. Lot coverage = building footprint ÷ lot area, shown as a percentage. Allowable floor area = lot area × FAR limit. Maximum footprint = lot area × coverage limit. Remaining = the limit minus what you have (existing plus proposed); a negative number means you are over.

Your local code decides what counts

This calculator does no zoning lookup and applies no definitions of its own. The limits, and what counts as floor area (basements, garages, attics, stairwells, covered porches) or as footprint or coverage (decks, driveways, accessory buildings), come from your municipality's zoning bylaw or code. Look them up there, enter only the areas your local code counts, and confirm the result with your planning or building department before you design or apply for a permit.

Source for the definitions used: ArchiDrop — FAR / GFA calculator (FAR is the ratio of total building floor area to site area; inputs are site area, permitted FAR and maximum site coverage). The generic formulas above are arithmetic; no third-party figures are built into this page.

Frequently asked questions

What is a good FAR?

There is no universal figure. FAR limits are set zone by zone in local codes. Enter yours from your bylaw.

Is FAR the same as lot coverage?

No. Coverage compares the building footprint to the lot (one level). FAR compares floor area on all levels to the lot, so a two-storey house can meet a coverage limit and still exceed a FAR limit.

Does the calculator store my numbers?

No. Everything is calculated in your browser and nothing is sent anywhere.

Arithmetic only — not zoning advice

This tool divides and multiplies the numbers you enter. It does not know your zoning, overlays, variances or how your municipality measures area. Confirm all limits and definitions with your local planning or building department.