Method 1: from the attic
- Hold a level against the underside of a rafter and bring the bubble to center, so the level is exactly horizontal.
- Mark 12 inches along the level, measured from the rafter.
- Measure straight up from the 12 inch mark to the underside of the rafter.
That vertical distance in inches is the pitch. If it is 6 inches, the roof is 6/12. Measure at two or three rafters to check the result.
Method 2: from a ladder at the eave
Place a ladder safely at the eave, hold a level against the roof surface with a 12 inch mark, and read the vertical drop as above. Never lean out or step off the ladder onto the roof. If the roof is steeper than about 6/12, skip this method.
Method 3: from the ground, using the gable end
Stand square to the gable wall and note two heights: the width of the house, and the height of the ridge above the top of the wall. Pitch = ridge height ÷ half the width × 12. For a 28 ft wide house, half the width is 14 ft. A ridge 7 ft above the top plate gives 7 ÷ 14 × 12 = 6, so a 6/12 roof. You can take the ridge height from a photo of the gable by using a known width as the scale.
Method 4: a phone angle app
Lay the phone along a rafter in the attic, or along a straight board laid on the roof surface, and read the angle. Convert to pitch with the degrees to pitch chart. Phone sensors are good to about a degree, which is enough to tell 4/12 (18.4°) from 6/12 (26.6°) but not 5/12 (22.6°) from 6/12 reliably.
What your reading probably means
| Vertical reading at 12 in | Pitch | Angle | Walkable? |
|---|---|---|---|
| 2 in | 2/12 | 9.5° | Yes, with care |
| 3 in | 3/12 | 14.0° | Yes, with care |
| 4 in | 4/12 | 18.4° | Yes, with care |
| 5 in | 5/12 | 22.6° | With caution when dry |
| 6 in | 6/12 | 26.6° | With caution when dry |
| 8 in | 8/12 | 33.7° | Not safely |
| 10 in | 10/12 | 39.8° | Not safely |
| 12 in | 12/12 | 45.0° | Not safely |
Once you have the reading, the roof pitch calculator gives the angle and area multiplier, and how to calculate roof pitch covers the formulas.
Frequently asked questions
How do I measure the pitch of my roof?
In the attic, hold a level against a rafter, mark 12 inches along it, and measure the vertical distance up to the rafter. That distance in inches is the pitch.
Can I measure roof pitch from the ground?
Yes. Divide the ridge height above the wall top by half the house width and multiply by 12, using the gable end.
Is a phone app accurate for roof pitch?
It is usually good to about one degree, which separates steep from shallow but can blur neighboring pitches such as 5/12 and 6/12.