About the Roof Pitch Calculator
Roof pitch describes how steep a roof is. In North America it is quoted as the rise in inches for every 12 inches of run, such as 6 in 12. Elsewhere the angle in degrees is common. This calculator takes the rise and the run, in any unit, and gives the pitch as a number in 12, the angle in degrees, the slope as a percentage and the rafter factor, a multiplier that turns horizontal distance into rafter length. Type the rise and the run and the roof pitch appears at once, with a few related figures underneath, and you can copy the result with one tap. The sums run in your browser, so nothing you enter is uploaded.
Updated October 2026
How to use the Roof Pitch Calculator
- 1Enter the rise and the run.
- 2Pick the units or options from the menus if the roof pitch tool offers them.
- 3Read the roof pitch in the large result box.
- 4Look at the extra rows for related figures.
- 5Press Copy result to keep the answer.
When you need the roof pitch
Roofers use pitch to choose materials, since tiles and shingles have minimum slopes. Builders use it to plan rafters, and designers use it to see how the loft space will look. Snow load and rain run-off also depend on the pitch.
A low pitch, below about 3 in 12, needs a membrane or other flat-roof systems. A steep pitch above 8 in 12 sheds snow easily but needs more material and safety gear when you work on it.
How the roof pitch is worked out
Pitch = rise ÷ run, shown as a number in 12. Angle = arctan(rise ÷ run). Slope percent = rise ÷ run × 100. Rafter factor = √(1 + (rise ÷ run)²). A roof that rises 6 inches over a 12 inch run has a 6 in 12 pitch. The angle is 26.57 degrees, the slope is 50 percent and the rafter factor is 1.118, so a rafter is 11.8 percent longer than its horizontal run. A 12 in 12 roof is a 45 degree roof.
Every answer on this page comes from that one rule, so you can check any result by hand with a calculator. The figures shown underneath, such as other units, are conversions of the same answer.
- Pitch, angle, slope and factor
- Any unit
- 12-inch reading
Mistakes to avoid with roof pitch
Use the same unit for rise and run. To get the standard x in 12 reading, enter 12 as the run. The angle is the pitch of the roof surface, which is not the same as the pitch of the rafter if the rafter has a birdsmouth cut. For the rafter length itself, use the Rafter Length Calculator.
On phone and computer
On a phone, type into the boxes one after another and read the roof pitch underneath; Copy result puts it on the clipboard for a message or a note. On a computer the inputs sit on the left and the answer on the right, so you can change one figure and watch the roof pitch move. The roof pitch calculator works the same on both. To find the length of each rafter, use the Rafter Length Calculator, and use the Angle Converter to switch between degrees and pitch units. For the roof surface size use the Roofing Calculator, and the Trigonometry Calculator works with the angles.
Features
- Enter 12 as the run
- Low pitches need special roofing
- Angle of the surface
- Clear messages when the roof pitch inputs make no sense
- Copy the result with one tap
- Private: nothing is uploaded
Frequently asked questions
How do I calculate roof pitch?
Pitch = rise ÷ run, shown as a number in 12. Angle = arctan(rise ÷ run). Slope percent = rise ÷ run × 100. Rafter factor = √(1 + (rise ÷ run)²). A roof that rises 6 inches over a 12 inch run has a 6 in 12 pitch. The angle is 26.57 degrees, the slope is 50 percent and the rafter factor is 1.118, so a rafter is 11.8 percent longer than its horizontal run. A 12 in 12 roof is a 45 degree roof.
What is the formula for roof pitch?
Pitch = rise ÷ run, shown as a number in 12. Angle = arctan(rise ÷ run). Slope percent = rise ÷ run × 100. Rafter factor = √(1 + (rise ÷ run)²). The roof pitch calculator applies it exactly and rounds only the displayed answer to six significant figures.
What is a 6/12 pitch in degrees?
26.57 degrees.
What pitch is 30 degrees?
About 6.9 in 12.
What is the rafter factor for?
Multiply the horizontal run by it to get the length of the rafter along the slope.
Is this roof pitch calculator free and private?
Yes. It is free, needs no account and runs in your browser, so the numbers you type are not uploaded or stored.