Pitch, slope and angle
They are one thing written three ways. A roof climbs a certain height for every foot it covers on the plan.
- Pitch says it the carpenter’s way: the inches of rise for every 12 in of run. A 6/12 roof climbs 6 in for each foot.
- Slope says it as a percentage: the rise divided by the run. 6/12 is 50%.
- Angle says it in degrees from the level: 6/12 is 26.57°.
Worked example. A 6/12 roof.
- Angle: the angle whose tangent is 6 ÷ 12, 26.57°
- Slope: 6 ÷ 12 = 50%
- Area multiplier: √(6² + 12²) ÷ 12 = 1.118
- Rafter length: 13.42 in for each foot of run
Going the other way, a roof at 30° is a 6.93/12 pitch: choose “Angle” and type the degrees.
How to measure roof pitch
You need a level and a tape, and you do not need to stand on the roof.
- In the attic. Hold the level against the underside of a rafter, flat. Mark 12 in along it from the end that touches, and measure straight up from that mark to the rafter. That figure in inches is the pitch.
- At a gable end. The same against the sloped trim of the gable, from a ladder.
- With any level. A short level works with a shorter run: choose “Rise and run” and enter both. A rise of 7 1/2 in over a run of 18 in is a 5/12 pitch, 22.62°.
Measure in two places. Old rafters sag, and a pitch read at the sag is not the pitch of the roof.
Pitch chart
| Pitch | Angle | Slope | Area multiplier |
|---|---|---|---|
| 1/12 | 4.76° | 8.3% | 1.003 |
| 2/12 | 9.46° | 16.7% | 1.014 |
| 3/12 | 14.04° | 25% | 1.031 |
| 4/12 | 18.43° | 33.3% | 1.054 |
| 5/12 | 22.62° | 41.7% | 1.083 |
| 6/12 | 26.57° | 50% | 1.118 |
| 7/12 | 30.26° | 58.3% | 1.158 |
| 8/12 | 33.69° | 66.7% | 1.202 |
| 9/12 | 36.87° | 75% | 1.250 |
| 10/12 | 39.81° | 83.3% | 1.302 |
| 11/12 | 42.51° | 91.7% | 1.357 |
| 12/12 | 45.00° | 100% | 1.414 |
Every figure is worked out from the pitch: the angle is the one whose tangent is the pitch over 12, and the multiplier is the length of the slope over one foot of run. The calculator shows the same chart with your own pitch in its place, also when it falls between two rows.
From pitch to roof area and squares
A roof is larger than the floor under it, and the multiplier says by how much. Take the footprint of the roof, overhangs included, and multiply: 1,200 sq ft at 6/12 is 1,342 sq ft of roof.
Roofing is sold by the square, which is 100 sq ft, and most shingles are packed 3 bundles to a square (IKO): that roof is 13.42 squares and 41 bundles, or 45 with 10% extra for the cuts. Enter the footprint under “Options” and the calculator does the same for yours.
A footprint and a pitch are enough for the shingles. For the sheathing, the drip edge and the ridge cap, “Plan the whole roof” opens the roofing calculator on the same pitch.
Low-slope roofs
Not every roofing goes on every pitch. Shingles shed water by overlapping, and below a certain slope water runs back under them; a shingle maker prints the lowest pitch its product may be laid on, and what has to go under it near that limit. Membranes and metal have limits of their own. Read the installation instructions of the product before you order it, and check your local code: the figure is theirs, not ours.
Questions about roof pitch
What is a 4/12 pitch in degrees?
18.43°, with an area multiplier of 1.054. A 12/12 roof is 45.00°, and its multiplier 1.414.
Is a 6/12 roof steep?
It is a middle pitch: 26.57°, half as much rise as run. Whether a roof can be worked on without staging is for the roofer standing on it to judge, with the weather and the roofing under their feet.
How do I convert pitch to degrees?
Divide the pitch by 12 and take the angle whose tangent that is: on a calculator, the key marked tan⁻¹ or atan. For 6/12, the tangent is 0.5 and the angle 26.57°.
How much bigger is the roof than the house?
By the multiplier of its pitch, on top of its overhangs: 1.054 at 4/12, 1.118 at 6/12, 1.202 at 8/12.
Sources
- IKO, How Many Square Feet in a Bundle of Shingles. A square is 100 sq ft of roof area. Most popular shingles are sold so that three bundles cover one square, but not all: read the label. Shingle waste is hard to predict; count on about 10 to 15 percent as a general range. Read on .
Updated . How we calculate. Found a mistake? Tell us.