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Roof Pitch Calculator

Enter the rise and run of the roof to get the pitch as x in 12, the angle in degrees, the percent slope, the rafter length with overhang and the multiplier that turns a footprint into sloped roof area. A 6 ft rise over 12 ft run is a 6/12 pitch, 26.57°, with a multiplier of 1.118.

Estimates only. Structural elements such as beams, footings, stairs, retaining walls over 1 m (4 ft) and rebar design must be designed or approved by a licensed engineer and comply with your local building code and permits. Results are "within typical limits", never "approved" — verify with your building authority.

Measurements

Units

Horizontal distance from the wall plate to the ridge.

Plan area including overhangs, to estimate the sloped roof area.

Results

Pitch

6/12

Angle

26.6 °

Slope
50 %
Rafter length
15.09 ft
Roof area multiplier
1.118
Show the working
  1. Slope6 ft ÷ 12 ft = 0.5 → 6/12
  2. Angleatan(0.5) = 26.57°
  3. Area multiplier√(1 + 0.5²) = 1.118
  4. Rafter length(12 ft + 18 in) × 1.118 = 15.09 ft
Paper and orientation
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How to use the roof pitch calculator

  1. Choose Imperial or Metric.
  2. Enter the rise (vertical height from plate to ridge).
  3. Enter the run (horizontal distance from plate to ridge, usually half the span).
  4. Enter the horizontal overhang past the wall.
  5. Optionally enter the roof footprint area to get the sloped roof area for ordering materials.

How the formulas work

Slope = rise ÷ run. Pitch = slope × 12 (inches of rise per foot of run). Angle = atan(slope). Percent slope = slope × 100. Multiplier = √(1 + slope²). Rafter length = (run + overhang) × multiplier. Sloped area = footprint × multiplier.

Worked examples

6/12 gable. Rise 6 ft, run 12 ft, 18 in overhang: pitch 6/12, 26.57°, 50% slope, multiplier 1.118, rafter length (12 + 1.5) × 1.118 = 15.09 ft.

Metric low-pitch roof. Rise 1.5 m, run 4 m, 450 mm overhang: slope 0.375, 4.5/12, 20.56°, multiplier 1.068, rafter 4.75 m.

Roof area. A 40 × 30 ft footprint including overhangs is 1,200 ft². At 6/12 the sloped area is 1,200 × 1.118 = 1,342 ft².

How to interpret the results

The pitch decides which roofing materials you can use and how much underlayment is needed. The sloped area is what roofing is priced on. Add waste for hips, valleys and starter courses.

Tips and common mistakes

  • Use the run, not the full span, for a gable roof.
  • Measure overhang horizontally; the calculator converts it along the slope.
  • Hip roofs have the same multiplier for each plane, but hip rafters are longer; this tool calculates common rafters only.
  • Check minimum pitch for your roofing product before deciding on a low slope.

Common roof pitches

Pitches are often described in words as well as numbers. A 4/12 roof rises 4 in per foot (about 18.4°) and is often called low slope for shingled roofs. A 6/12 roof (26.6°) is a moderate pitch that is comfortable to work on. A 12/12 roof rises one foot per foot, 45°, and is steep enough to need roof brackets or harnesses for most work. The calculator gives the exact angle for any pitch, which you need for setting a saw or a bevel gauge.

Assumptions and limitations

Rafter sizes, spacing and connections are structural and must follow span tables or an engineer’s design and local codes. The tool does not calculate snow or wind loads.

Frequently asked questions

How do I calculate roof pitch?

Divide the rise by the run and multiply by 12 to get the pitch in inches per foot. A 6 ft rise over 12 ft run is 0.5 × 12 = 6, a 6/12 pitch.

How do I convert pitch to degrees?

Take the arctangent of rise ÷ run. A 6/12 pitch is atan(0.5) = 26.57°. A 12/12 pitch is 45°.

What is the roof area multiplier?

It is the ratio of sloped length to horizontal length: √(1 + (rise ÷ run)²). Multiply the plan footprint by it to get the sloped surface area. For 6/12 it is 1.118.

How long are the rafters?

Rafter length = (run + overhang) × the multiplier. This is the line length along the top of the rafter, before plumb and seat cuts.

What run should I use?

For a symmetrical gable, the run is half the building span, measured from the outside of the wall plate to the centre of the ridge.

Is a steeper pitch better?

Steeper roofs shed water and snow faster but cost more in materials and labour. Roofing products specify minimum pitches, so check the manufacturer’s requirements.

Sources