Six units of rise for every twelve of horizontal run, which is about 26.6 degrees. The convention of using twelve makes pitches directly comparable.

Construction & HomestructuralUnited States only

Roof Pitch Calculator

Roof pitch as an angle, a percentage and an area multiplier. The multiplier is the number that matters when ordering material, because a pitched roof is always larger than the footprint beneath it.

Also called: roof slope calculator, rise over run.

Roof area multiplier

1.12

A 6:12 pitch is 26.57 degrees, and the sloped roof is 1.12 times the footprint. On a 120 footprint that is 134.16 of actual roof.

Angle (degrees)

26.57

Rafter length per unit of run

13.42

Footprint area

120

Sloped roof area

134.16

Slope as a percentage

50%

How this is calculated

Method and background

How this is calculated

Pitch is quoted as rise over run, conventionally per twelve. The rafter is the hypotenuse, so the ratio of rafter to run is the factor by which the sloped area exceeds the plan area. A 6:12 pitch adds about twelve percent, and a 12:12 adds forty-one. Ordering roofing against the footprint is the most common way to run short, which is why the multiplier is the headline here.

the multiplier is the rafter length over the horizontal run

rise: Vertical rise
run: Horizontal run

Worked examples

Each of these is asserted on every build. If a change to the engine ever moved one of these answers, the build would fail before the page could print it.

a six in twelve pitch

Rise: 6
Run: 12
Building width: 10
Building length: 12

Roof area multiplier1.12

atan(0.5) and sqrt(180)/12, computed independently

Open this example

a flat roof has a multiplier of one

Rise: 0
Run: 12
Building width: 10
Building length: 12

Roof area multiplier1

boundary

Open this example

Method and limits

What it assumes

A simple gable. Hips and valleys add cutting waste beyond this.

What it deliberately does not model

Overhangs are not included in the footprint.

Formula version 1.0.0 · definition 1.0.0 · United States · Report a problem with this calculator

Frequently asked questions

What does 6:12 mean?: Six units of rise for every twelve of horizontal run, which is about 26.6 degrees. The convention of using twelve makes pitches directly comparable.