Roof Area Calculator
A free, browser-based calculator. Runs entirely in your browser — no sign up, nothing stored.
100% FreeRuns in your browserBasic
Enter Values
Enter your values and press Calculate to see results.
How to use this calculator
- Enter the footprint area and the roof pitch (rise and run).
- Read the sloped roof area.
How it works
The slope factor is √(rise² + run²) ÷ run. Multiplying the flat footprint by it gives the actual sloped surface area.
Worked example
100 m² footprint, 4:12 pitch. Slope factor ≈ 1.054, so roof area ≈ 105 m².
Common mistakes
- Using the footprint as the roof area — a pitched roof is always larger.
- Forgetting overhangs, hips, valleys and waste when ordering material.
Frequently asked questions
What's a roof pitch like 4:12?
It rises 4 units for every 12 of horizontal run — enter 4 as rise and 12 as run.
Related tools
Tip: Enter any known values to calculate the remaining results.
All calculations run in your browser. Your inputs are never saved or transmitted.