How to calculate roof pitch
Enter the roof measurements, then read the pitch, angle, slope, and rafter values in the Result section. Each field can use a different unit. The page lists the converted values and formulas used for the calculation.
- Enter the vertical measurement in Rise (vertical height).
- Enter the horizontal measurement in Run (horizontal distance). For a simple gable, measure from the outside wall to the ridge center line, often half the building span.
- Enter Overhang (optional), or leave it at
0when the rafter length should stop at the wall line. - Select
in,ft,cm, ormfor each field, then select Calculate. - Read Result. Select Copy result for the text summary, Download result (.txt) to save it, or Reset to restore the defaults and hide the result.
What the roof pitch calculator shows
The Result section lists Roof pitch as X/12, Roof angle from horizontal in degrees, Slope (grade percent), and Rafter length in feet. The assumptions table includes the entered rise and run, inch conversions, overhang in inches, and the common and overhang rafter lengths.
Rise: 6 in
Run: 12 in
Overhang: 0 in
Roof pitch: 6/12
Roof angle: 26.565 degrees from horizontal
Slope (grade percent): 50%
Common rafter length: 1.118 ftThe formula appears as one block above the assumptions table. Copy result places the summary in the clipboard when the page can access it. Download result (.txt) creates a plain-text file.
Roof pitch formula and overhang
The calculator converts Rise (vertical height), Run (horizontal distance), and Overhang (optional) to inches before calculating:
Roof pitch (X/12) = (Rise / Run) x 12Angle = atan(Rise / Run)Slope % = (Rise / Run) x 100Rafter length = sqrt(Rise^2 + (Run + Overhang)^2)
Overhang changes the rafter-length calculation only. The calculator adds it to Run (horizontal distance) before finding the hypotenuse. Roof pitch, angle, and slope use Rise (vertical height) divided by Run (horizontal distance). With 0 overhang, the two rafter-length values match.
Input limits and rafter length
Rise (vertical height) accepts 0.01 through 600 in its selected unit. Run (horizontal distance) accepts 0.01 through 1200, and Overhang (optional) accepts 0 through 240. A blank, non-numeric, non-finite, or out-of-range value shows an error instead of a result.
- Rafter length is a straight theoretical common-rafter length.
- The calculation does not adjust for ridge board thickness, birdsmouth or seat cuts, hip or valley rafters, loads, lumber sizing, material quantities, or building codes.
- Displayed and exported numbers use fixed decimal places.
Where roof pitch calculations come up
A homeowner can check a gable roof's pitch before discussing a repair or reroofing plan. A carpenter can add the eave overhang and compare the straight rafter length with the common length before laying out cuts.
A drafter can switch units when measurements arrive in feet, centimeters, or meters, then copy the result into a project note. Angle and slope percent record the same roof geometry in different forms.
Which construction calculator to use
This calculator is for roof geometry. It is part of Construction Calculators. Choose the Roofing Calculator for roofing material quantities based on roof dimensions, pitch, coverage, and waste.
Choose the Construction Materials Calculator for roofing plus other material modes. Choose the Lumber Calculator for board feet and total lumber cost.
Frequently Asked Questions
How do I calculate roof pitch from rise and run?
Divide rise by run and multiply by 12 to get roof pitch as X/12. A rise of 6 in over a run of 12 in produces a 6/12 pitch.
What do Rise and Run mean in a roof pitch calculator?
Rise (vertical height) is how far the roof climbs. Run (horizontal distance) is the horizontal distance used for that rise. For a simple gable, Run (horizontal distance) reaches from the outside wall toward the ridge center line.
How does Overhang change rafter length?
Overhang (optional) is added to Run (horizontal distance) before the calculator finds the hypotenuse. It changes the displayed rafter length, while pitch, angle, and slope still use the original Rise (vertical height) and Run (horizontal distance).
Can I use different units for rise and run?
Yes. Rise (vertical height), Run (horizontal distance), and Overhang (optional) each have their own unit selector for in, ft, cm, or m.
What does this roof pitch calculator leave out?
It leaves out building-code lookups, structural or engineering determinations, lumber sizing, material quantities, ridge-board deductions, and cut allowances. The output uses the values entered in the form.