How to find the pitch of a roof: three ways with a level and a tape
Hold a level against the roof or a rafter, mark 12 inches along it, and measure straight up or down from that mark to the roof. That measurement in inches is the pitch: 6 inches is a 6/12 pitch, which is 26.6 degrees and a 50% slope.
Anthony Hicks30+ years in construction. Updated November 5, 2026.
Reading as
What pitch means
Pitch is how many inches a roof rises for every 12 inches it runs level. A 6/12 roof (said “six twelve” and sometimes written 6:12) climbs 6 inches for each foot from the eave toward the ridge. The run is always 12, so the rise alone names the pitch.
Three ways to measure it
You need a level at least 12 inches long and a tape measure.
1. In the attic
- Find a rafter and hold the level against its underside, one end touching the rafter.
- Level it, bubble centered, and mark the level at 12 inches from that end.
- Measure straight up from the 12 inch mark to the bottom of the rafter.
That measurement is the rise. A 6 inch measurement is a 6/12 pitch.
2. At a gable end, from a ladder
Hold the level against the rake board (the sloped trim at the gable) the same way, level it, and measure from the 12 inch mark up to the board. This is the safest way that doesn’t need an attic.
3. On the roof
Set one end of the level on the shingles, level it, and measure from the 12 inch mark straight down to the roof. Only on a roof that’s safe to walk, and with fall protection.
With a phone
A phone’s level reads the angle. On an iPhone, the Measure app has a level that shows how many degrees a surface is off level (Apple calls the reading approximate): hold the phone’s edge against the roof or a rafter. The roof pitch calculator turns degrees into the pitch.
From the outside, without a ladder
If the ridge’s height above the walls and the building’s width are known, the pitch follows: the run is half the width. A 24 foot wide house with the ridge 6 feet above the top of the walls has 6 feet of rise over 12 feet of run, a 6/12 pitch.
Pitch, degrees and percent
| Pitch | Angle | Slope | Roof area factor |
|---|---|---|---|
| 3/12 | 14.0° | 25% | 1.031 |
| 4/12 | 18.4° | 33% | 1.054 |
| 5/12 | 22.6° | 42% | 1.083 |
| 6/12 | 26.6° | 50% | 1.118 |
| 7/12 | 30.3° | 58% | 1.158 |
| 8/12 | 33.7° | 67% | 1.202 |
| 9/12 | 36.9° | 75% | 1.250 |
| 10/12 | 39.8° | 83% | 1.302 |
| 12/12 | 45.0° | 100% | 1.414 |
- Angle = the arctangent of rise ÷ run.
- Slope = rise ÷ run × 100.
- Roof area factor = how much bigger the sloped roof is than the flat footprint under it: √(rise² + 12²) ÷ 12. Multiply a footprint by it for the roof’s area.
Why pitch matters
- Rafters. A rafter is its run times the pitch’s area factor, plus the tail; the rafter calculator works out the length and the cuts.
- Area and materials. A steeper roof has more area over the same house. The roofing calculator uses the pitch to count squares and bundles.
- What can go on it. Asphalt shingles need at least 2/12, and from 2/12 up to 4/12 the code calls for two layers of underlayment (IRC R905.2.2). Below 2/12, a roof needs a low-slope membrane.
- Walking and safety. Steep roofs need roof jacks, harnesses and more time, which shows up in the price.
Common questions
What is the angle of a 6/12 roof?
26.6 degrees (26.57 to two places).
What pitch is 22.5 degrees?
About 5/12: 12 × tan(22.5°) is 4.97 inches of rise per foot.
How high is a 12/12 roof?
A 12/12 roof rises as far as it runs, so the ridge sits half the building’s width above the walls: 12 feet up on a 24 foot wide house.
Can I measure roof pitch with my phone?
Yes. A phone’s level app reads the angle when its edge sits on the roof or a rafter, and the angle converts to a pitch. The roof pitch calculator does the conversion.
What’s the lowest pitch for shingles?
2/12. Asphalt shingles aren’t allowed below that, and from 2/12 up to 4/12 they need two layers of underlayment (IRC R905.2.2).