Roof Slope and Coating Thickness Calculator

Calculate your roof's slope (pitch ratio and angle) and determine the recommended coating thickness based on slope and coating type.

Vertical Rise (inches):

Horizontal Run (inches, typically 12):

Roof Area (sq ft):

Coating Type:

Number of Coats:

Coverage Rate (sq ft / gallon): Leave blank to use coating-type default

Pitch Ratio: Pitch = Rise ÷ Run

Slope Angle: θ = arctan(Rise ÷ Run) × (180 ÷ π)

Slope Factor: SF = √(Rise² + Run²) ÷ Run

Actual Roof Area: A_actual = A_plan × SF

Slope Adjustment Factor: SAF = min(1 + 0.005 × max(θ − 14°, 0), 1.25)

Adjusted WFT per Coat: WFT_adj = WFT_base × SAF

Total DFT: DFT_total = DFT_adj/coat × Number of Coats

Theoretical Coverage: Cov = 1604.17 ÷ WFT_adj (sq ft/gal)

Total Gallons: G = (A_actual ÷ Coverage Rate) × Coats × 1.10

Run is conventionally 12 inches (standard US pitch notation); adjust as needed.
Slope classification follows NRCA (National Roofing Contractors Association) guidelines.
Base WFT/DFT values per coat are industry averages per ASTM D6083 (acrylic), ASTM C1127 (silicone), and typical manufacturer TDS data.
Slope adjustment of +0.5% per degree above 14° accounts for coating sag and drainage on steeper surfaces, capped at +25%.
Theoretical coverage formula: 1 US gallon = 231 in³; 1 mil = 0.001 in; 1 ft² = 144 in² → 231 ÷ (0.001 × 144) ≈ 1604.17 sq ft·mil/gal.
A 10% material waste factor is applied to account for overspray, surface irregularities, and equipment loss.
DFT (Dry Film Thickness) assumes typical volume solids: ~70% for elastomeric/acrylic, ~80% for silicone, ~80% for polyurethane, ~80% for bitumen, ~80% for epoxy.
Always verify with the coating manufacturer's Technical Data Sheet (TDS) for project-specific requirements.
This calculator does not account for primer coats, substrate porosity, or environmental conditions (temperature, humidity).

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