Formula
How this estimate works
slope percent = rise / run x 100
A 4:12 pitch is about a 33.3% slope because the roof rises 4 inches over a 12 inch horizontal run.
Slope percent and pitch
Slope percent is rise divided by run, multiplied by 100. A 4:12 pitch is about a 33.3% slope, while steeper roof pitches produce higher slope percentages.
When slope matters
Roof slope affects drainage, material suitability, installation method, and surface area. Check product requirements for low-slope roofs.
Assumptions used
- Pitch is shown as inches of rise per 12 inches of horizontal run.
- Rafter length uses the same units entered for rise and run.
- Pitch multiplier estimates sloped surface area from flat footprint area.
Before you order materials
- Use slope percent for comparison, not as a direct material quantity.
- Confirm minimum slope for roofing products.
- Use pitch multiplier for surface area planning.
Frequently asked questions
What is a 4:12 roof slope percentage?
A 4:12 pitch is about 33.3% slope because the roof rises 4 inches for every 12 inches of horizontal run.
Is slope percent the same as pitch?
No. Pitch is usually shown as rise per 12 inches of run, while slope percent is a percentage.
Why is low slope important?
Some roofing materials require minimum slope for drainage and warranty compliance.