Enter the rise and run (or the angle) and get the standard pitch, roof angle, slope percentage
and rafter length — updated live as you type.
What is roof pitch?
Roof pitch describes how steep a roof is. In the US it is written as the number of inches the
roof rises vertically for every 12 inches of horizontal run — so a roof that rises 6 inches
per foot of run has a 6/12 pitch. The same steepness can also be expressed as
an angle in degrees or as a slope percentage, and this calculator converts between all three.
How to calculate roof pitch
Pitch is the ratio of rise to run, normalized to a run of 12:
pitch = (rise ÷ run) × 12
angle = atan(rise ÷ run)
slope % = (rise ÷ run) × 100
rafter length = √(rise² + run²) — per unit of run
To measure an existing roof, hold a 12″ level horizontally against the roof (or a rafter in
the attic) and measure straight down from its free end to the surface. That distance in
inches is your pitch over 12.
Roof pitch to angle conversion chart
| Pitch | Angle | Slope | Rafter multiplier |
|---|
| 1/12 | 4.8° | 8.3% | 1.0035 |
| 2/12 | 9.5° | 16.7% | 1.0138 |
| 3/12 | 14.0° | 25.0% | 1.0308 |
| 4/12 | 18.4° | 33.3% | 1.0541 |
| 5/12 | 22.6° | 41.7% | 1.0833 |
| 6/12 | 26.6° | 50.0% | 1.1180 |
| 7/12 | 30.3° | 58.3% | 1.1577 |
| 8/12 | 33.7° | 66.7% | 1.2019 |
| 9/12 | 36.9° | 75.0% | 1.2500 |
| 10/12 | 39.8° | 83.3% | 1.3017 |
| 11/12 | 42.5° | 91.7% | 1.3566 |
| 12/12 | 45.0° | 100.0% | 1.4142 |
| 13/12 | 47.3° | 108.3% | 1.4743 |
| 14/12 | 49.4° | 116.7% | 1.5366 |
| 15/12 | 51.3° | 125.0% | 1.6008 |
| 16/12 | 53.1° | 133.3% | 1.6667 |
| 17/12 | 54.8° | 141.7% | 1.7341 |
| 18/12 | 56.3° | 150.0% | 1.8028 |
The rafter multiplier is the rafter length per foot of horizontal run.
Multiply it by your run (half the building span for a gable roof) to get the rafter length,
then add the overhang.
Frequently asked questions
What is a 4/12 roof pitch?
A 4/12 pitch means the roof rises 4 inches vertically for every 12 inches of horizontal run. It equals an angle of about 18.4° and a slope of 33%. It is one of the most common pitches on modern homes.
What is the minimum roof pitch for shingles?
Asphalt shingles require a minimum pitch of 2/12. Between 2/12 and 4/12, most codes and manufacturers require a double underlayment or a self-adhering ice-and-water membrane. Below 2/12 you need a membrane or metal roof system designed for low slopes.
How do I measure the pitch of my existing roof?
Hold a 12-inch level horizontally against the roof surface (or against a rafter in the attic). Measure straight down from the free end of the level to the roof surface — that measurement in inches is your pitch over 12. For example, 6 inches means a 6/12 pitch.
What roof pitch is walkable?
Pitches up to about 6/12 (26.6°) are generally considered walkable with care. Between 7/12 and 9/12 you need roof jacks or scaffolding, and 10/12 or steeper is considered non-walkable and requires professional safety equipment.
How do I convert roof pitch to degrees?
Angle = arctangent(rise ÷ run). For a pitch of x/12: angle = atan(x/12). For example, 8/12 = atan(8 ÷ 12) = 33.7°.
What is the most common roof pitch?
Most residential roofs in North America fall between 4/12 and 9/12. 6/12 is a popular compromise — steep enough to shed water and snow well, while still being relatively safe to work on.