Roof Pitch Calculator
Convert roof slope (Rise/Run) to exact degrees, area multipliers, and rafter cut lengths.
Roof Slope Inputs
Roof Pitch to Degrees Conversion Chart
Every standard pitch from 1/12 to 12/12, with the exact angle, slope percentage, and the area multiplier used to convert a footprinted ground area into true roof surface area. Angles follow atan(rise ÷ 12).
| Pitch | Angle (Degrees) | Slope % | Area Multiplier | Rafter per 12" Run | Classification |
|---|---|---|---|---|---|
| 1/12 | 4.76° | 8.3% | 1.003 | 12.04" | Flat / membrane only |
| 2/12 | 9.46° | 16.7% | 1.014 | 12.17" | Low slope — double underlayment |
| 3/12 | 14.04° | 25.0% | 1.031 | 12.37" | Low slope — walkable |
| 4/12 | 18.43° | 33.3% | 1.054 | 12.65" | Shallow — easy to walk |
| 5/12 | 22.62° | 41.7% | 1.083 | 13.00" | Walkable |
| 6/12 | 26.57° | 50.0% | 1.118 | 13.42" | Standard |
| 7/12 | 30.26° | 58.3% | 1.158 | 13.89" | Standard |
| 8/12 | 33.69° | 66.7% | 1.202 | 14.42" | Steep — use jacks/planks |
| 9/12 | 36.87° | 75.0% | 1.250 | 15.00" | Steep |
| 10/12 | 39.81° | 83.3% | 1.302 | 15.62" | Very steep |
| 11/12 | 42.51° | 91.7% | 1.357 | 16.28" | Very steep |
| 12/12 | 45.00° | 100% | 1.414 | 16.97" | 45° — harness required |
Rafter length per foot of run = √(12² + rise²). Multiply your horizontal run by this factor to get the actual rafter board length before any overhang or ridge adjustments.
Understanding Roof Pitch
In construction, roof pitch is expressed as the number of vertical inches a roof rises for every 12 inches it extends horizontally. For example, a 6:12 pitch rises 6 inches vertically for every 12 inches of horizontal run.
Frequently Asked Questions
What is a 6/12 roof pitch in degrees?
A 6/12 (or 6:12) roof pitch equals an angle of 26.57 degrees. Its slope area multiplier is 1.118, meaning a roof surface is 11.8% larger than its ground footprint.
What is the most common residential roof pitch?
The most common roof pitches in North America range from 4:12 (18.43°) to 9:12 (36.87°). Pitches below 3:12 are considered low-slope and require special double-underlayment or rolled roofing membrane.
How do you calculate true roof area from pitch?
Measure the flat horizontal ground footprint of the house (e.g., 2,000 sq ft) and multiply it by the roof pitch multiplier (for a 6/12 pitch, multiplier is 1.118). 2,000 sq ft × 1.118 = 2,236 sq ft of actual roof surface area.
What pitch is a 30-degree roof?
A 30-degree angle is almost exactly a 7/12 pitch (30.26°). To convert any angle to pitch, multiply 12 by the tangent of the angle: 12 × tan(30°) = 6.93 inches of rise, which rounds to the nearest standard pitch of 7/12.
What is the minimum roof pitch for asphalt shingles?
Per the IRC (R905) and manufacturer specifications, asphalt shingles require at least a 2/12 pitch installed with double underlayment layers. From 4/12 and steeper, a single underlayment layer is standard. Below 2/12 you must switch to a rolled membrane, modified bitumen, or standing-seam metal system.
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