Key takeaways
- You can usually measure pitch from the attic, without going on the roof.
- You only need a level and a tape: mark 12 inches level, then measure straight up to the rafter.
- A phone angle reading converts to pitch with tangent × 12.
Pitch is how many inches a roof rises for every 12 inches of level distance. You can find it with a level and a tape measure, and you usually don't need to go on the roof at all.
Safety first. Falls from roofs and ladders can kill. Use the attic or ground methods if you can. If you have any doubt about a ladder or roof, ask a roofer to measure instead.
Method 1: from the attic (best)
- Hold a level flat against the underside of a rafter, keeping the level horizontal.
- Mark the level 12 inches from where it touches the rafter.
- At that mark, measure straight up to the bottom of the rafter.
That vertical measurement is your pitch. If it's 7 inches, your roof is 7/12.
Method 2: from a ladder at the gable end
If your roof has an exposed gable edge, you can do the same thing from a securely placed ladder without stepping onto the roof.
- Hold the level horizontally against the rake board or trim.
- Measure 12 inches along the level.
- Measure straight up from that point to the roof edge.
Method 3: from a phone or angle reading
Many phones include or can add a level app that reads an angle. Place the phone on a rafter from inside the attic, then convert the angle:
Pitch = tan(angle) × 12
For example, 30° gives 0.577 × 12, or about 6.9/12. Check the reading twice, because phone cases and rough rafters can throw it off.
If your measurement isn't over 12 inches
Any rise and run will work, as long as they use the same units. Divide the rise by the run, then multiply by 12. A rise of 5 inches over a run of 24 inches is 5 ÷ 24 × 12, or 2.5/12. The roof pitch calculator does this for you.
Measure each section
Additions, porches and dormers often have a different pitch from the main roof. Measure each one, then work out each section's area separately with the roof area calculator.
Mistakes that throw off the reading
- Measuring along the slope. The 12 inches must be level, not along the rafter.
- Letting the level drift. Check the bubble again before you take the vertical measurement.
- Measuring a sagging rafter. Take readings on more than one rafter, and away from any obvious sag.
- Using trim that isn't parallel to the roof. Rake boards and fascia can be misleading on older homes, so the attic is more reliable.
- Assuming one pitch for the whole roof. Measure additions and porches separately.
What to do with your reading
| Your reading | Next step |
|---|---|
| Below 2/12 | The model code doesn't allow asphalt shingles here. See minimum pitch. |
| 2/12 up to 4/12 | Double underlayment applies to shingles under the 2021 IRC. |
| 4/12 and up | Use the roof area calculator to work out materials. |
| Two readings disagree | Measure a third rafter, or ask a roofer. |
Frequently asked questions
Do I need to go on the roof to measure pitch?
Usually not. The attic method measures the rafters directly from inside.
What tools do I need?
A level at least 12 inches long, or a shorter level with a straight board, plus a tape measure. A pencil makes it easier to mark the 12-inch point.
Does OSHA's fall protection rule apply to homeowners?
OSHA's rules cover employees, but they're a useful benchmark. For workers, fall protection rules apply on roofs with unprotected edges 6 feet or more above a lower level.
Sources
We use primary sources where we can: building codes, federal rules and manufacturer documents. Read our editorial standards.
- OSHA fall protection for roofing work: 29 CFR 1926.501(b)(10) and (11)