Building footprint & slope
Include the eave overhang; shape factor lets you tweak hips or complex forms.
Length runs along the eaves; width runs along the ridge. Overhang adds both sides.
Roof planes
Break the roof into planes with horizontal length/width, slope, and count.
Known roof area
Use this if you already know the paintable roof area before exclusions.
Exclusions (skylights, fixtures)
Subtract openings that will not be painted.
Paint settings
Pick finish, substrate, coats, waste, and primer. You can override coverage if needed.
Coverage overrides (optional)
Leave these fields blank to use the built-in coverage and absorption presets for typical roof coatings.
How the roof area estimate works
- Plan (horizontal) area comes from the building footprint (including overhang) or the roof planes you enter.
- Slope factor converts plan area to sloped surface area based on pitch (rise/run).
- Exclusions (skylights, fixtures, other) are subtracted to get the paintable area.
- Paint volume uses paintable area ÷ coverage, then multiplies by coats, waste, and absorption (primer is calculated separately).
Worked example (US units)
Suppose your plan area is 1,344 ft², pitch is 4/12 (slope factor ≈ 1.054), and exclusions total 50 ft². Paintable area ≈ 1,344×1.054 − 50 ≈ 1,367 ft². With topcoat coverage 250 ft²/gal, 2 coats, and 12% waste, topcoat ≈ (1,367 ÷ 250) × 2 × 1.12 ≈ 12.3 gallons.
Safety note: measure from drawings or from the ground when possible. Avoid climbing on roofs for measurements.
Frequently asked questions
How accurate are these roof paint estimates?
They are planning values only. Results combine your roof dimensions, slope factor, exclusions, coverage presets, absorption factor, coats, and waste allowance. Real projects vary with product formulation, weather, and surface condition. Always follow the paint label and size up if unsure.
Can I override coverage or primer settings?
Yes. Turn primer on or off, change coats, and override coverage or absorption values when your product differs from the built-in presets. The calculator ships with typical roof coating presets; if your product label lists different coverage, enter those numbers in the override fields.
Comments
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