Roof Pitch Calculator
A 6:12 roof rises 6 inches for every 12 inches of horizontal run. That is 26.6 degrees, a 50 percent slope, and a pitch multiplier of 1.1180, meaning the roof surface is about 12 percent larger than the ground area it covers.
Enter a rise and run below, or an angle, or a percentage, and everything else updates instantly. It works in both directions.
Convert a roof's rise and run into pitch, degrees, percentage slope and the roof pitch multiplier. Everything updates as you type, and it works backwards too, so you can enter degrees and get the pitch.
What this means
Using the pitch multiplier
The multiplier converts a flat footprint into the real sloped surface area. Multiply the horizontal area covered by the roof by the multiplier and you get the area you actually have to cover with roofing.
It is secant of the roof angle, or √(rise² + run²) ÷ run, the hypotenuse of the slope triangle divided by its base.
Pitch reference
Need the roof measured properly?
Pitch is one number on a roof that usually has several: most homes have more than one plane, and the steep one is rarely the one you can see from the drive. We measure every plane and give you the real figures.
Get Your Roof Measured Working out material quantities? Try the roofing squares and materials calculator.The formulas
- Pitch (X:12) = rise ÷ run × 12
- Angle in degrees = arctan(rise ÷ run)
- Percentage slope = rise ÷ run × 100. A 12:12 roof is 45° and 100% slope, the point where the two scales cross.
- Pitch multiplier = √(rise² + run²) ÷ run, which is the secant of the roof angle.
- Low slope conventionally means below 4:12 for shingle installation rules, and below 2:12 most codes require a low-slope membrane rather than shingles at all. Above about 8:12 a roof is generally not walkable and crews need fall protection and roof jacks, which is why steeper roofs cost more to work on.
What the pitch multiplier is for
The multiplier converts a flat footprint into real roof area. Multiply the horizontal area a roof covers by the multiplier and you get the sloped surface you actually have to cover with roofing material.
This is the step people skip when they estimate a roof from a property record, and it is why those estimates always come in low. A 2,000 square foot footprint under a 6:12 roof is about 2,236 square feet of roof (22.4 roofing squares rather than 20).
Mathematically it is the secant of the roof angle, or √(rise² + run²) ÷ run, the hypotenuse of the slope triangle divided by its base.
Why pitch changes what a roof costs
- Below 2:12, most codes will not permit shingles at all; a low-slope membrane such as TPO or modified bitumen is required.
- Between 2:12 and 4:12, shingles are permitted but manufacturers require a doubled underlayment layer. Skipping that is a common and expensive shortcut.
- From about 4:12 to 7:12 is the comfortable middle of residential roofing: walkable, standard installation, no slope premium.
- From 8:12 upward a roof stops being reliably walkable. Crews use roof jacks and staging, work slows down, and the labour rate rises.
- Above 12:12 full fall protection and staging are required throughout, material handling is slower, and the cost premium is significant.
How to find your roof pitch safely
From the attic: hold a level horizontally against the underside of a rafter, mark 12 inches along it, and measure straight up from that mark to the rafter. That measurement is your rise over a 12 run.
From outside: a gable end often lets you measure the rise and run of the roof line from a ladder at the eave, or estimate it against a known reference. A phone level app held flat against a rafter in the attic will also give you the angle directly.
Do not climb onto the roof to measure pitch. There is no version of this measurement that is worth the risk, and every method above avoids it.
Frequently asked questions
What is a 6:12 roof pitch in degrees?
A 6:12 pitch is 26.6 degrees from horizontal. It is also a 50 percent slope, and it carries a pitch multiplier of 1.1180, so the roof surface is about 12 percent larger than the footprint beneath it. It is one of the most common residential pitches in Austin.
What is the roof pitch multiplier?
It is the number you multiply a roof's horizontal footprint by to get its actual sloped surface area. It equals √(rise² + run²) ÷ run, which is the secant of the roof angle. A 4:12 roof has a multiplier of 1.054, a 6:12 is 1.118, a 9:12 is 1.250 and a 12:12 is 1.414.
How do I measure my roof pitch without getting on the roof?
From inside the attic: hold a level horizontally against the underside of a rafter, mark 12 inches along the level, then measure vertically from that mark up to the rafter. That vertical measurement is your rise over a 12-inch run. A phone level app held against a rafter gives you the angle directly.
What pitch is considered a low-slope roof?
Below 4:12 is generally treated as low slope for shingle installation purposes, where manufacturers require doubled underlayment. Below 2:12, most codes do not permit shingles at all and a low-slope membrane system is required instead.
What is the steepest roof you can walk on?
Around 7:12 is the practical limit for most people, and crews commonly treat 8:12 as the point where roof jacks and staging become necessary. Above that the roof is not reliably walkable and the labor cost rises accordingly, which is why steep roofs carry a premium on any quote.