It's how steep a roof is, written as inches of vertical rise per 12 inches of horizontal run. A 4/12 is a gentle slope; a 12/12 rises at 45 degrees. Enter rise and run above to get yours.

How do I convert roof pitch to an angle?

Take the arctangent of rise divided by run. A 6/12 pitch is about 26.6 degrees, a 12/12 is 45. The calculator shows the angle automatically.

How do I find rafter length?

It's the hypotenuse of the triangle formed by rise and run: the square root of rise squared plus run squared. Enter your rise and run and the tool returns the rafter length directly.

Why does pitch matter for ordering materials?

A steeper roof has more actual surface than its flat footprint, so you need the slope multiplier to order the right amount of shingles or sheathing. This calculator gives you that multiplier.

Roof Pitch Calculator: Pitch, Angle & Rafter Length

Roof pitch, and why it changes your material order

Pitch is how steep a roof is, written as inches of rise over 12 inches of run. It decides your rafter length, whether you can walk the roof, and how much bigger the roof is than the house under it. This tool turns a rise and run into the pitch as x-in-12, the angle in degrees, the slope as a percent, the rafter length, and the multiplier that converts a footprint into real roof area.

How pitch is written and measured

A 6/12 pitch rises 6 inches for every 12 inches across. To measure one you don't have on paper, hold a level out from the roof, mark 12 inches along it, and measure straight down to the roof at that point. That drop is your rise over 12. It's the same number a framer and a roofer both work from.

The conversions, and a table to skip them

The angle is the arctangent of rise over run. The percent is rise divided by run times 100. The area multiplier, the one that matters for ordering, is the square root of the rise-over-run squared plus one. Here are the common ones worked out.

Pitch	Angle	Percent	Area multiplier	Walkable
3/12	14.0°	25%	1.031	Yes
4/12	18.4°	33%	1.054	Yes
6/12	26.6°	50%	1.118	Yes, with care
8/12	33.7°	67%	1.202	Hard
12/12	45.0°	100%	1.414	No, staging needed

Turn a footprint into actual roof area

This is the number that orders shingles. The flat area your roof covers on the ground, times the pitch multiplier, gives the true sloped area you have to cover. A 1,200 square foot footprint at 6/12 is 1,200 times 1.118, about 1,342 square feet of roof. Divide by 100 for roofing squares, so about 13.4 squares, then add waste and round up to order.

Rafter length

A common rafter is the long side of a right triangle, so its length is the square root of the rise squared plus the run squared. Add your overhang past the wall, and subtract half the ridge board's thickness at the peak. For a 15-foot run at 6/12, the rise is 7.5 feet and the rafter works out near 16.8 feet before the overhang.

What the pitch means for the job

Anything up to about 6/12 is walkable for most people, so you can work off the roof itself. Past 8/12 you're into roof jacks and staging, which adds time and cost. On the low end, standard shingles want at least a 4/12; you can go down to 2/12 only with a doubled underlayment, and below that you're into membrane or metal, not shingles.

Roof pitch by the numbers

Pitch	Angle	Multiplier	Notes
3/12	14.0°	1.031	Minimum for most shingles
4/12	18.4°	1.054	Common low-slope ranch
6/12	26.6°	1.118	The suburban standard
8/12	33.7°	1.202	Steep; harness territory
12/12	45.0°	1.414	A-frames, steep gables

The multiplier is the working number: footprint area times multiplier equals true roof area. A 1,600-square-foot footprint at 6/12 is really 1,789 square feet of shingles, and missing that difference under-orders a full square and a half.

Quick answers

How do I measure pitch without going on the roof? From inside the attic: level held against a rafter, measure up 12 inches out, then the vertical rise. Or measure the gable end from the ground with a photo and a level line.

What pitch needs special shingles? Below 2/12, shingles are out and membrane roofing is in. Between 2/12 and 4/12, shingles need doubled underlayment per most manufacturers.

Does pitch change the shingle order? Twice over: more true area, and steeper roofs waste more in cuts and staging. Our roof measuring guide walks the whole takeoff.