Roof Pitch Calculator
Convert roof pitch to angle in degrees and get the rafter length multiplier.
How this calculator works
angle = arctan(rise ÷ 12) · multiplier = √(rise² + 144) ÷ 12
The multiplier is the number that converts a flat footprint into actual sloped roof area, and horizontal run into true rafter length. A 6/12 roof has a multiplier of 1.118, so its surface is 11.8% larger than the ground it covers.
Worked example
With rise 6 in, this calculator returns 26.57 °.
Roof pitch to angle conversion chart
Figures below assume . Change any measurement in the calculator to get your own numbers.
| Rise | Roof angle (°) | Rafter / area multiplier | Slope |
|---|---|---|---|
| 1 in | 4.76 | 1.00 | 8.33 |
| 2 in | 9.46 | 1.01 | 16.67 |
| 3 in | 14.04 | 1.03 | 25.00 |
| 4 in | 18.43 | 1.05 | 33.33 |
| 5 in | 22.62 | 1.08 | 41.67 |
| 6 in | 26.57 | 1.12 | 50.00 |
| 7 in | 30.26 | 1.16 | 58.33 |
| 8 in | 33.69 | 1.20 | 66.67 |
| 9 in | 36.87 | 1.25 | 75.00 |
| 10 in | 39.81 | 1.30 | 83.33 |
| 12 in | 45.00 | 1.41 | 100.0 |
| 16 in | 53.13 | 1.67 | 133.3 |
| 18 in | 56.31 | 1.80 | 150.0 |
| 24 in | 63.43 | 2.24 | 200.0 |
Rise is per 12 inches of run. The multiplier converts a flat footprint area into actual roof surface area — multiply your footprint square footage by it.
What roof pitch is right for what
| Type | Typical pitch (rise per 12) | Notes |
|---|---|---|
| Low-slope membrane (EPDM, TPO) | 1.00 | Below 2/12, shingles are not permitted |
| Minimum for asphalt shingles | 2.00 | Requires doubled underlayment below 4/12 |
| Standard shingle roof | 4.00 | Walkable, the most common residential pitch |
| Conventional gable roof | 6.00 | Walkable with care; sheds snow well |
| Steep — staging required | 8.00 | Above this, crews cannot walk the roof |
| Victorian, chalet, A-frame | 12.00 | 45 degrees; needs roof jacks and harnesses throughout |
| Mansard upper slope | 3.00 | Nearly flat above a very steep lower slope |
| Alpine or heavy-snow region | 18.00 | Sheds snow load before it accumulates |
Pitch drives cost as much as material does. Every step above 8/12 adds staging, slows the crew and increases the roof area for the same footprint.
Roof pitch questions
What does 6/12 pitch mean?
The roof rises 6 inches for every 12 inches of horizontal run. It is the standard way US builders express pitch, and it works out to an angle of 26.6 degrees.
How do I convert roof pitch to degrees?
Take the arctangent of rise divided by 12. A 4/12 roof is 18.4 degrees, 6/12 is 26.6, 9/12 is 36.9, and 12/12 is exactly 45 degrees.
What is the roof pitch multiplier used for?
It converts flat measurements into sloped ones. Multiply the building footprint by it to get true roof area, or multiply the horizontal run by it to get rafter length. For 6/12 the multiplier is 1.118.
What is considered a walkable roof pitch?
Up to about 6/12 most roofers will walk without staging. From 7/12 to 9/12 needs roof jacks, and anything above 10/12 requires proper fall protection. Labour rates climb sharply with pitch for this reason.
How do I measure roof pitch from inside the attic?
Hold a level horizontally against a rafter, mark 12 inches along it, then measure vertically from that mark up to the rafter underside. That vertical distance is the rise per 12 — no need to get on the roof.
Is roof pitch the same as slope?
Not quite. Pitch is expressed as rise per 12 inches of run. Slope is usually given as a percentage — a 6/12 pitch is a 50% slope, and 26.57 degrees. All three describe the same roof.
What is the most common roof pitch?
Between 4/12 and 6/12 on US houses. That range sheds water reliably, stays walkable for maintenance, and keeps the roof area close to the building footprint.
Does roof pitch affect how much material I need?
Yes, through the multiplier. A 4/12 roof needs 5.4% more material than its footprint, a 12/12 roof needs 41.4% more. On a large roof that difference is thousands of dollars.
What is the minimum pitch for asphalt shingles?
Manufacturers require 2/12 as an absolute minimum, and between 2/12 and 4/12 you must use a double layer of underlayment. Below 2/12 shingles will leak and you need a membrane roof instead.