How to calculate roof pitch
Measure rise and run in the same units, then scale the result to a 12 inch run. A 6 inch rise over 12 inches of run is a 6/12 roof pitch.
Pitch, slope, and angle are related
Roof pitch is usually written as rise over 12. Slope can also be shown as percent or angle. For example, 4/12 is about 18.4 degrees and 6/12 is about 26.6 degrees.
Measure safely
Use building plans, attic measurements, or ground-level methods when possible. Do not climb onto an unsafe roof to collect measurements for a calculator.
Common roof pitch checks
Pitch is rise per 12 inches of run. Use plans or safe measurements; do not climb onto unsafe roofs for calculator inputs.
| Pitch | Approx. angle | Area multiplier |
|---|---|---|
| 4/12 | 18.4 degrees | 1.054x footprint |
| 6/12 | 26.6 degrees | 1.118x footprint |
| 8/12 | 33.7 degrees | 1.202x footprint |
| 12/12 | 45 degrees | 1.414x footprint |
Before you calculate
- Measure rise and run consistently, commonly using inches of rise over 12 inches of run.
- Use the same roof section for both measurements.
- Check separate roof planes when the roof has more than one pitch.
Common mistakes
- Confusing pitch ratio, slope percentage, and angle degrees.
- Measuring along the roof surface instead of using rise and horizontal run.
- Applying one pitch to a roof with multiple planes.
Formula
pieces = ceil((length * (1 + wastePercent / 100)) / pieceLength)
Assumptions
- Default slope is about 1 inch per 16.67 feet.
- Local conditions may require different slope.
- This is a planning estimate only.
Example
Estimated gutter drop needed: 3 in drop
How to calculate gutter slope in drop
- Measure the total run length in feet.
- Enter the usable length per piece, roll, board, strip, or section.
- Add waste for cuts, overlaps, corners, and damaged pieces.
- Divide adjusted length by usable piece length and round up to whole units.
- Keep fasteners, connectors, corners, end caps, and layout hardware as separate checks.
Before you buy materials
- Use pitch results as context for material planning, not as a final roof measurement.
- Verify roof pitch safely from plans or with a qualified roofer when access is risky.
FAQ
What is the example gutter slope in drop result?
Use total run length, usable unit length, and waste, then calculate the planning result. In the default example, the result is 3 in drop.
What is a 6/12 roof pitch?
A 6/12 pitch means the roof rises 6 inches for every 12 inches of horizontal run. It is about 26.6 degrees.
How do I convert roof pitch to angle?
Use angle = arctangent(rise / run). For a 4/12 pitch, arctangent(4 / 12) is about 18.4 degrees.
Does roof pitch calculate roof area?
No. Pitch is a slope relationship. Roof material quantity still needs roof area, waste, and product coverage.
Should I climb on the roof to measure pitch?
No. Use plans, attic framing, or a qualified roofer when measurements cannot be taken safely.
Related calculators
This calculator is for planning estimates only. Verify final quantities with product labels, project conditions, and a qualified professional when accuracy matters.