How to use this calculator
- Enter your own values in the labeled fields. Check the units and assumptions before comparing results. Only the fields needed for your selected calculation mode are shown.
- Your answer updates automatically. Review the calculation steps to see exactly how it was calculated.
- Copy, share, save, or download your result. Saved inputs stay on this device.
How the calculation works
Use horizontal roof footprint including overhangs. A uniform slope factor converts it to sloping area, then the allowance increases the required coverage. A roofing square is 100 square feet; pack coverage comes from the selected product. Review the units, period and assumptions before comparing scenarios. Displayed values are rounded, while the underlying calculation retains its available precision.
A worked example
A 1,000 ft² footprint at 0/12 pitch with 10% allowance needs 1,100 ft² or 11 roofing squares.
Reading your result
Use the main result together with its units and supporting figures. Display values are rounded; calculations keep their underlying precision. A change in inputs or assumptions can change the answer. Compare the step-by-step working with your intended use before relying on an estimate.
Frequently asked questions
What assumptions does this calculation use?
Use horizontal roof footprint including overhangs. A uniform slope factor converts it to sloping area, then the allowance increases the required coverage. A roofing square is 100 square feet; pack coverage comes from the selected product.
Can I save or check a scenario?
The result includes the working and supporting values. Save and Restore keep inputs on this device; Copy, Download and Print export the result. Sharing a scenario explicitly includes the inputs in its link.
Sources & methodology
This calculator uses the mathematical identity and assumptions stated above. No current rates, prices, or external data are loaded. Conversion tools use international unit definitions.
Formula review: October 24, 2026. Read our methodology.