Roof Pitch Calculator
Calculate the roof angle in degrees and the slope as a percentage, from rise (vertical height) and run (horizontal length).
How to use the calculator
- Measure or find the rise — the vertical height the roof climbs over a given length.
- Measure or find the run — the horizontal length the rise is measured over.
- See the roof angle in degrees and the slope as a percentage.
How it's calculated
Roof pitch is sometimes given in degrees, sometimes as a slope percentage (rise/run × 100), and in some English-language sources as a ratio "X:12" (rise in inches per 12 inches of run). This calculator shows both degrees and percentage — both describing the same geometric relationship.
Pitch sets limits on the roofing material
The angle of a roof is not purely an aesthetic choice. Every roofing material has a minimum pitch specified by its manufacturer, because water has to run off fast enough for the overlap between tiles or sheets to stay watertight. Roof tiles generally need a steeper pitch than corrugated sheeting, and below a certain angle you have to move to a membrane system that does not rely on fall at all.
Snow load pulls in the opposite direction to what many people assume. A steep roof sheds snow more readily, while a shallow roof accumulates it — which means a higher design load on the structure. In snowy regions this is one reason traditional roofs are steep, and it is also why snow load is calculated from both location and roof pitch.
Frequently asked questions
What's the difference between roof angle in degrees and slope in percent?
Both describe the same slope, just on different scales. 45° corresponds to 100% slope (rise = run), while a shallow angle near 0° gives a slope near 0%.
What roof pitch works for roof tiles?
This varies by product and manufacturer guidance — many tile types require a minimum pitch (often around 18-22°) to stay watertight. Check the product's technical specification.
Can I use this calculator for a ramp or staircase?
Yes, the formula for angle and slope is the same whether it's a roof, a ramp, or another sloped surface.