Roof Pitch Calculator
Convert between rise/run, degrees, and x/12 roof pitch, and compute rafter length with overhang.
Processed locally in your browser — nothing is uploaded.
Roof Pitch Calculator
Inches of rise per 12 in of run
Usually half the building width — leave blank to skip
Results
- Pitch
- 6/12
- Angle
- 26.57°
- Slope
- 50%
- Pitch multiplier
- 1.118
Sloped length per foot of horizontal run
Rafter length is plumb-cut to plumb-cut along the slope; add for ridge boards and seat cuts.
About Roof Pitch Calculator
Start from whichever number you have — a measured rise and run, a pitch like 6/12, or an angle in degrees — and get all three plus the slope percentage and pitch multiplier. Add a horizontal run and overhang to get the rafter length via the Pythagorean theorem.
Common uses
- Translate a 26.6° measurement into a 6/12 pitch
- Cut rafters to length for a shed roof with a 1 ft overhang
- Find the pitch multiplier for shingle takeoffs
Example
Input
Pitch 6/12, run 12 ft, 1 ft overhang
Output
26.57° · 50% slope · multiplier 1.118 · rafter 14.53 ft
Limitations
- Rafter length is the plain slope diagonal — ridge-board thickness and birdsmouth cuts are extra
Frequently asked questions
What angle is a 6/12 roof pitch?
26.57 degrees. The conversion is arctan(rise ÷ run): a 4/12 pitch is 18.43°, 8/12 is 33.69°, and 12/12 is exactly 45°.
What is a roof pitch multiplier?
The factor that converts a roof's flat footprint into its true sloped area: √(1 + (pitch/12)²). A 6/12 roof has a multiplier of 1.118, meaning every 100 sq ft of footprint is 111.8 sq ft of actual roof surface.
How do I measure the pitch of an existing roof?
Hold a level horizontally against the roof (or a rafter in the attic), mark 12 in along it, and measure straight down from that mark to the surface — that vertical distance in inches is your rise per 12, e.g. 6 in means a 6/12 pitch. Enter the rise and run here to get the angle and slope.
How do I calculate rafter length from the pitch?
Multiply the horizontal run (plus any level overhang) by the pitch multiplier — the Pythagorean theorem in disguise. A 12 ft run with a 1 ft overhang at 6/12 gives 13 × 1.118 = 14.53 ft; add extra for the ridge-board offset and birdsmouth before cutting.
Are the numbers I enter sent to a server?
No. All the pitch, angle, and rafter math runs in your browser — measurements are never transmitted or stored.