Roof Pitch Calculator

Enter the rise and run of a roof to get its pitch as x/12, its angle in degrees, its percent slope and the rafter length. Everything runs in your browser and nothing is sent anywhere.

Mode

Unit label (display only)

Rise (vertical height)

Run (horizontal distance)

Enter your values and press Calculate.

How to use this roof pitch calculator

Choose a mode. Use “Rise + run to pitch” if you measured the vertical rise and the horizontal run. Use “Pitch + run to rise” if you already know the pitch, such as 6/12, and want the rise for a given run.
Pick a unit label (inch, ft, cm or m). It is only a label and does not convert anything, so measure rise and run in the same unit.
Type your numbers. The run is the horizontal distance the roof covers, and the rise is how far it climbs over that run.
Press Calculate or the Enter key. Press Reset to clear everything and start again.

How to calculate roof pitch

Roof pitch compares how much a roof climbs (the rise) with how far it travels horizontally (the run). In the United States it is usually written as a ratio over 12, so a 6/12 roof rises 6 units for every 12 units of run. The calculator uses these formulas:

Pitch (x/12) = rise / run x 12
Angle = arctan(rise / run), shown in degrees
Percent slope = rise / run x 100
Rafter length = square root of (run squared + rise squared). This is the length along the slope for the run you entered and does not include overhang.
Rise from pitch (second mode) = pitch / 12 x run

Some common pitches and what they work out to: 4/12 is 18.43 degrees (33.33% slope), 6/12 is 26.57 degrees (50%), 8/12 is 33.69 degrees (66.67%), 9/12 is 36.87 degrees (75%) and 12/12 is 45 degrees (100%).

Worked example

Say a simple gable roof sits on a building that is 24 ft wide. Each side of the roof covers half the width, so the run is 12 ft. If the ridge is 6 ft above the top of the walls, the rise is 6 ft. Pitch = 6 / 12 x 12 = 6, so the roof is 6/12. Angle = arctan(6 / 12) = 26.57 degrees. Percent slope = 6 / 12 x 100 = 50%. Rafter length along the slope = square root of (12 x 12 + 6 x 6) = square root of 180, which is about 13.42 ft.

For the second mode, a 6/12 pitch over a 20 ft run gives a rise of 6 / 12 x 20 = 10 ft.

Assumptions & limits

The roof is treated as a single flat plane with a straight slope. Hips, valleys, dormers and curved roofs need to be worked out section by section.
The rafter length is the straight-line length along the slope for the run you entered. It does not include overhang, the ridge board, birdsmouth cuts or waste, so ask your builder or supplier how much extra to allow.
The result is only as accurate as your measurements. Round-off is shown to two decimals.
This is a maths tool, not construction advice. Typical minimum pitches for roofing materials vary by material and by local rules, so check the manufacturer’s instructions and your local building rules before you decide anything.

Frequently asked questions

What is a 6/12 roof pitch?

It means the roof rises 6 units for every 12 units of horizontal run. That is an angle of about 26.57 degrees, or a 50% slope.

How do I measure rise and run?

Hold a level horizontal, mark 12 inches along it, and measure straight up or down from that point to the roof surface. That gives the rise for a 12 inch run. If you are not comfortable on a roof, measure from the attic along the underside of a rafter instead of climbing up.

Is roof pitch the same as roof angle?

No. Pitch is a ratio such as 6/12, while the angle is measured in degrees. The two describe the same slope in different ways, and the calculator shows both.

What does the rafter length include?

Only the straight-line length along the slope for the run you entered. Overhang, cuts and waste are not included.

Which unit should I use?

Any unit works as long as rise and run use the same one. The pitch, angle and percent slope are the same whether you measure in inches, feet, centimetres or metres.

What pitch do I need for my roofing material?

That depends on the material, the manufacturer’s instructions and local rules, so check those first. This calculator only turns your measurements into pitch, angle, slope and length.