Method 1: level and tape
A 2 ft level and a tape give the pitch directly. Set the level on the roof or against a rafter, make it level, and measure the vertical gap from the 12 in mark to the roof surface or rafter edge.
Five ways to measure roof pitch
- Level and tape on the roof surface (from a ladder at the eave).
- In the attic: the same method against the underside of a rafter, with no climbing.
- Speed square: put the pivot on the rafter edge, swing the square until the body is plumb, and read the pitch on the common scale.
- Phone angle app: lay the phone on a rafter or the roof and read the angle; convert below.
- From the gable end: measure the rise from the wall plates to the ridge and half the building width, then divide rise by run and multiply by 12.
Roof angle calculator: degrees to pitch
To turn an angle into a pitch, pitch = 12 × tan(angle). Use the table, or the roof pitch calculator for any value:
| Angle | Pitch (rise per 12) | Nearest whole pitch |
|---|---|---|
| 10° | 2.12 | 2/12 |
| 14° | 2.99 | 3/12 |
| 18.43° | 4 | 4/12 |
| 20° | 4.37 | 4/12 |
| 22.62° | 5 | 5/12 |
| 25° | 5.6 | 6/12 |
| 26.57° | 6 | 6/12 |
| 30° | 6.93 | 7/12 |
| 33.69° | 8 | 8/12 |
| 35° | 8.4 | 8/12 |
| 40° | 10.07 | 10/12 |
| 45° | 12 | 12/12 |
Check the pitch against the roofing
Using the pitch for rafters and roof area
The pitch you measure turns level dimensions into sloped ones. Rafter length is the level run times √(1 + (pitch ÷ 12)²), and roof area is the footprint times the same factor; the IRC measures rafter spans on that horizontal projection too[2]. So a 6/12 pitch measured in the attic tells you that every foot of run takes 13.42 in of rafter, and every 100 sq ft of footprint is 111.8 sq ft of roof. The rafter calculator and the roof truss calculator take it from there.
Once you have the pitch, check it against the roofing: asphalt shingles need at least 2/12 and, up to 4/12, double underlayment (IRC R905.2.2)[1]. Common pitches are compared on the 4/12 roof pitch page, and the roof calculator turns the pitch into roof area.
Stay safeThe attic and gable-end methods give the same pitch without walking on the roof.
Frequently asked questions
How do you find the pitch of a roof?
Measure the vertical rise over 12 in of level run. With a level and tape, the rise in inches at the 12 in mark is the pitch.
Can I measure roof pitch from the ground?
Yes, from the gable: rise from the wall plates to the ridge ÷ half the building width × 12. A phone angle app on a rafter also works.
How do I convert roof angle to pitch?
Pitch = 12 × tan(angle). 30° is 6.93/12 and 45° is 12/12.
How do you measure roof pitch with a speed square?
Hold the pivot on the rafter edge, rotate the square until the body is plumb, and read the pitch where the rafter edge crosses the common scale.