Roof calculators
Free tools for planning work on a low-slope commercial roof. They run in your browser and show their formulas and sources.
- Roof coating calculatorEstimate the gallons and 5-gallon pails of roof coating you need from roof area, the dry mils your spec requires and the product's volume solids.
- Roof drain calculatorFind your ZIP code's 100-year, 1-hour rainfall rate, the flow in gallons per minute your roof drains must carry, and how many drains it takes.
Updated October 2026.