How to measure roof pitch
Roof pitch is the rise in inches for every 12 inches of horizontal run — a "6 in 12" roof climbs 6 inches per foot. You can measure it in about two minutes with a level and a tape, and you don't have to get on the roof to do it. Here are three ways, plus a chart that turns pitch into degrees.
What "pitch" means
Pitch is written as rise : 12 — the first number is how many inches the roof rises over a fixed 12 inches of run. So 4:12 is gentle, 12:12 is a dramatic 45°. Because the run is always 12, you only ever have to measure one thing: the rise.
Method 1 — A level and a tape (easiest)
This is the standard way and works from inside the attic, no ladder onto the roof required:
- Hold a level horizontally against the underside of a rafter (or against the roof surface if you're up there safely).
- Bring the bubble to level.
- Measure straight down from the 12-inch mark on the level to the rafter or roof. That distance is your rise.
If the tape reads 6 inches at the 12-inch mark, your pitch is 6:12. Using a short torpedo level? Measure at its end and scale up — 3 inches of drop over a 6-inch level is the same as 6 over 12.
Method 2 — A speed square or pitch gauge
A rafter (speed) square has a pivot point and degree markings. Rest it against the roof or a rafter, let it hang to level, and read the angle — or use a dedicated pitch gauge, which shows the rise-in-12 directly. Quick and accurate once you've done it once.
Method 3 — Your phone
Most phones have a level / inclinometer built into the compass or measure app, and free "bubble level" apps add one. Lay the phone flat on the roof surface (or on a board set on the shingles) and read the angle in degrees, then convert with the chart below. It's the fastest method when you're already up on a low roof.
Pitch, angle & slope factor
The slope factor is what you multiply a roof's footprint by to get its true surface area:
| Pitch | Angle | Slope factor | Feel |
|---|---|---|---|
| 2:12 | 9.5° | 1.014 | Low-slope |
| 4:12 | 18.4° | 1.054 | Walkable |
| 6:12 | 26.6° | 1.118 | Walkable (common) |
| 8:12 | 33.7° | 1.202 | Getting steep |
| 10:12 | 39.8° | 1.302 | Steep |
| 12:12 | 45.0° | 1.414 | Very steep |
Have your rise and run?
The roof pitch calculator turns rise and run into pitch, angle, slope percent, slope factor, and rafter length — instantly.
Open the Roof Pitch CalculatorWhy pitch matters
- Material quantity. A steeper roof has more area than its footprint — multiply by the slope factor before ordering shingles.
- What roofing is allowed. Standard asphalt shingles generally need at least a 4:12 pitch (2:12 with special double underlayment). Below that, you're into low-slope membrane territory.
- Safety. Most people can move on a roof up to about 6:12; past 8:12 you'll want roof jacks, staging, or a harness — or a pro.