What this calculator does
This tool turns your measurements into a consistent planning estimate you can review before pricing or starting work. It is useful during early takeoffs, option comparisons, and on-site checks where transparent math matters.
How the calculation works
Formula
Pitch = rise ÷ run. Angle = arctan(rise ÷ run). The X:12 result multiplies that ratio by 12.Worked example
A 6-inch rise over a 12-inch run is a 6:12 pitch, a 26.57° angle, and a 50% slope.
How to measure
- 01Measure rise and run using the same unit.
- 02Keep the level run horizontal—not along the roof surface.
Common mistakes to avoid
- Mixing inches and feet
- Measuring the sloped length as run
- Rounding before the final step
Limits of this estimate
This geometry does not evaluate roof structure, loading, drainage, or local rules.
Frequently asked questions
Is 6:12 the same as 50%?
Yes. Six divided by twelve is 0.5, or a 50% slope.
Can rise and run be in centimetres?
Yes. The ratio is unitless as long as both use the same unit.