Free site coverage tool
Add roofs, driveways, patios, walks and proposed hardscape to estimate impervious coverage and remaining permeable area.
Enter the project measurements, then select Calculate. Nothing is uploaded or stored.
How to use the calculator
Impervious coverage can include roofs, concrete, asphalt, compacted areas, pool decks and other surfaces that limit water infiltration. Definitions and credits for permeable materials vary, and stormwater rules may apply separately.
Continue your permit planning
Calculation questions
These answers explain the planning calculation. Verify local definitions before using the result in a permit package.
Roofs, asphalt, concrete, paved parking and many patios are commonly included. Gravel, pools and permeable pavers are treated differently by different codes.
Not always. Building coverage focuses on structures, while impervious coverage can include structures plus paved and hardscape surfaces.
Some jurisdictions provide partial or full credit when an approved permeable system is installed. Product choice alone does not guarantee an exclusion.
It helps reviewers evaluate drainage, stormwater runoff and open-space compliance. Projects near the limit may require additional documentation or design changes.
Need drawings, not just a calculation?
Send the property address, proposed project and any city checklist. We will confirm the drawing scope before you order.
Calculation methodology reviewed August 2026 · Educational planning tool, not a zoning determination or survey.
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