Roof Pitch Calculator

Slope, Angle & Rise/Run Conversion

How do you calculate roof pitch?

Hold a 12-inch level against a rafter, bring it level, and measure straight down from the 12-inch mark to the rafter. That drop in inches is the rise over a 12-inch run. A 6-inch drop is a 6/12 pitch — 26.57 degrees, a 50% slope, and a 1.1180 area multiplier.

The Roof Pitch Calculator converts a roof rise and run measurement into the standard X-in-12 pitch ratio, the angle in degrees, and the slope multiplier used to convert flat footprint area to actual sloped surface area. Pitch directly affects how much shingle and underlayment material you need, what waste factor to apply, whether you can walk the roof safely, and which materials are even allowed by code. Use this tool together with our Roof Area Calculator and Pitch Chart to size every other material on your roof.

Roof pitch is the rise in inches over 12 inches of horizontal run. A 6/12 pitch rises 6 inches for every foot it travels sideways. That single ratio decides the angle you are working at, how much surface area sits above a given footprint, which materials the code allows, and whether the roof is safe to walk.

Every pitch, converted

The multiplier is the number that matters for ordering material: multiply the flat footprint area by it to get the actual sloped surface you have to cover.

Roof pitch converted to angle, slope percentage and area multiplier
Pitch	Angle	Slope %	Multiplier	2,000 sq ft footprint becomes
1/12	4.8°	8.3%	1.0035	2,007 sq ft
2/12	9.5°	16.7%	1.0138	2,028 sq ft
3/12	14.0°	25.0%	1.0308	2,062 sq ft
4/12	18.4°	33.3%	1.0541	2,108 sq ft
5/12	22.6°	41.7%	1.0833	2,167 sq ft
6/12	26.6°	50.0%	1.1180	2,236 sq ft
7/12	30.3°	58.3%	1.1577	2,315 sq ft
8/12	33.7°	66.7%	1.2019	2,404 sq ft
9/12	36.9°	75.0%	1.2500	2,500 sq ft
10/12	39.8°	83.3%	1.3017	2,603 sq ft
12/12	45.0°	100.0%	1.4142	2,828 sq ft
14/12	49.4°	116.7%	1.5366	3,073 sq ft
16/12	53.1°	133.3%	1.6667	3,333 sq ft
18/12	56.3°	150.0%	1.8028	3,606 sq ft
20/12	59.0°	166.7%	1.9437	3,887 sq ft
24/12	63.4°	200.0%	2.2361	4,472 sq ft

A 2,000 sq ft footprint at 6/12 is 2,236 sq ft of roof — 236 sq ft more shingle than the footprint suggests, which is most of an extra square.

How to measure pitch without getting on the roof

Hold a 12-inch level against a rafter in the attic, level it, then measure straight down from the 12-inch mark to the rafter. That drop in inches is the rise.
From the ground, photograph the gable end square-on and measure the rise and run on the photo — the ratio survives the scaling.
A speed square with a pitch scale read against a level gives the same answer in one step.
Phone level apps read the angle in degrees; convert with the table above rather than guessing.

Common mistakes when measuring pitch

Measuring the rafter length instead of the vertical rise. The rise is the drop over a level 12 inches, not the distance along the timber.
Using a level that is not actually level. A quarter-inch of error over 12 inches changes a 6/12 reading to a 6.25/12.
Measuring one slope on a roof that has two. Gambrel and saltbox roofs have a different pitch on each face and each face needs its own figure.
Reading a degree number off a phone app and treating it as the pitch. 26.57 degrees is 6/12; the two scales are not interchangeable.

What pitch decides on the rest of the job

Pitch is the first number you need because almost everything else depends on it. It sets the area multiplier, so it sets how much shingle, underlayment and sheathing you buy. It decides whether asphalt shingles are permitted at all, and whether they need a doubled underlayment layer. It drives the labour rate, because work above 9/12 needs staging and everything has to be carried rather than slid. And it changes the waste factor, because steeper roofs take more cuts and produce more offcuts.

Get the pitch wrong by a single increment and every downstream number is wrong with it. On a 2,000 square foot footprint, reading 6/12 when the roof is actually 8/12 leaves you about 60 square feet short — enough to stop the job for a day.

Frequently asked questions

What is a 6/12 roof pitch in degrees?

A 6/12 pitch is 26.57 degrees. It rises 6 inches for every 12 inches of horizontal run, which is a 50% slope and an area multiplier of 1.1180.

What is the most common residential roof pitch?

Most American homes fall between 4/12 and 9/12. Below 4/12 shingles need extra underlayment protection; above 9/12 the roof is no longer comfortably walkable.

How do I measure roof pitch from inside the attic?

Hold a 12-inch level against the underside of a rafter, bring it level, then measure straight down from the 12-inch end to the rafter. That measurement in inches is the rise over a 12-inch run.

What is the minimum pitch for asphalt shingles?

Two in twelve. Between 2/12 and 4/12 most manufacturers require a doubled underlayment layer. Below 2/12 shingles are not permitted and you need a membrane roof.