Lot Coverage Calculator
Lot coverage (%) = counted ground footprint ÷ lot area × 100. Enter your lot in square feet or acres, add the footprints your local definition counts, and compare a proposed project with your entered limit.
1. Lot and existing footprints
Use ground-level area in square feet, not floor area across stories. Count each area once; do not add a garage again if it is already included in the main building.
2. Compare your project
How to calculate coverage: percentage or materials?
For percentage coverage, divide the covered area by total area and multiply by 100. For example, 2,000 sq ft covered on a 10,000 sq ft lot is 20%.
If you mean material coverage, use quantity and installed depth instead. One cubic yard of gravel or mulch covers 108 sq ft at 3 inches before allowance. Sod uses the supplier’s square-foot coverage per piece or pallet.
Choose the matching tool: gravel coverage, mulch coverage, or sod pallet coverage. The building calculator above uses counted ground footprints and your entered local limit.
What is lot coverage?
Lot coverage is counted ground footprint divided by lot area, multiplied by 100. The local definition determines which buildings, covered areas or other surfaces belong in the numerator. A 2,200 sq ft footprint on a 10,000 sq ft lot is 22% coverage.
This calculator adds your areas; it does not detect overlapping shapes, identify your zoning district or supply a legal limit. Use the map tool to estimate lot area and the property planner to explore space and geometry separately.
Example: building coverage on a half-acre lot
A 0.5-acre lot has 21,780 sq ft. A 2,000 sq ft house footprint plus a separate 400 sq ft garage gives 2,400 ÷ 21,780 × 100 ≈ 11.02% coverage. Adding a 600 sq ft footprint raises it to about 13.77%.
If your own planning scenario uses a fictional 20% limit, the allowance is 4,356 sq ft and the remaining arithmetic allowance after that project is 1,356 sq ft. This does not establish a local legal limit or a buildable location.
Coverage, impervious surface and floor area are different inputs
| Question | Area to identify | What to check |
|---|---|---|
| Building or lot coverage | Counted ground footprints | Local treatment of garages, sheds, covered porches and decks |
| Impervious surface coverage | Surfaces counted as impervious | Local treatment of roofs, driveways and paving |
| Floor area ratio (FAR) | Counted floor area across levels | Separate floor-area definition and exclusions |
This tool compares the ground footprints you enter. Check the applicable definitions before using an allowance. See our calculation methods and limits.
How much coverage allowance remains?
Allowance in sq ft = lot area × entered limit ÷ 100.
Remaining allowance = allowance − existing counted footprints − new counted footprint. A negative result is an excess above the entered limit.
Worked example: adding a garage
Start with a 10,000 sq ft lot, a 1,800 sq ft house and a separate 400 sq ft garage. Existing coverage is (1,800 + 400) ÷ 10,000 × 100 = 22%. Suppose your planning scenario uses a fictional 30% limit: that gives a 3,000 sq ft allowance and 800 sq ft remaining before a project.
| Scenario | Counted footprint | Coverage | Comparison with 3,000 sq ft |
|---|---|---|---|
| Existing buildings | 2,200 sq ft | 22% | 800 sq ft remaining |
| Add 600 sq ft | 2,800 sq ft | 28% | 200 sq ft remaining |
| Add 900 sq ft | 3,100 sq ft | 31% | 100 sq ft above the limit |
The 30% figure is an example, not a USA-wide standard or a rule for your address. A positive remainder does not tell you where a building can go. Check garage footprint and clearance, access, easements and your local requirements separately.
Choose the right areas before calculating
- Use footprint, not living area. A second floor usually changes total floor area without doubling the ground footprint.
- Avoid overlap. Do not enter an attached garage separately if the main footprint already includes it. Overlapping roofs or structures require measurements consistent with the applicable rule.
- Keep definitions separate. Building coverage and impervious surface coverage may count different features. Do not treat the uncounted remainder as lawn or permeable land.
- Use the right lot denominator. Confirm how the applicable rule defines lot area, as well as the coverage percentage.
For an example of why definitions matter, Seattle's addition and remodel guidance discusses combined structures, covered areas and certain decks. It is an illustration of local variation, not the rule for every property. See our calculation methodology for the tool's broader limits.
Frequently asked questions
Is lot coverage the same as floor area ratio (FAR)?
No. Lot coverage compares ground footprint with lot area. FAR generally compares total floor area across levels with lot area.
Do driveways count toward lot coverage?
It depends on the local zoning code. Some jurisdictions distinguish building coverage from impervious surface coverage.
Can I use acres instead of square feet?
Yes. Choose Acres in the lot area unit field; the calculator converts the denominator to square feet using 1 acre = 43,560 sq ft. Keep building and project footprints in square feet. Changing the unit preserves the lot area you have already entered.
Does remaining allowance mean I can build that much?
No. It is the arithmetic difference from the limit you entered. Setbacks, access, easements, height, other coverage rules and approvals can further restrict a project.
Coverage, open land and project fit
A remaining coverage allowance does not locate usable space. Read how to estimate usable land, then include the full project envelope and clearance when testing a garage, pool or shed.