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Roof Pitch Calculator

Enter the rise and run to get your roof pitch, angle, grade and slope multiplier, with a pitch-to-angle chart and the formula shown.

Updated
Reading time2 min
Sources verified

Key takeaways

  • Pitch is the inches of rise per 12 inches of level run, so a 6/12 roof rises 6 inches every foot.
  • The slope multiplier turns a level footprint into sloped roof area.
  • OSHA treats anything above 4/12 as a steep roof.

Enter any rise and run you've measured, in the same units. They don't need to be a 12-inch run: the calculator scales them to the standard "per 12" form.

  • Roof pitch6/126 inches of rise per 12 inches of run
  • Angle and grade26.6° · 50%
  • Slope multiplier1.118Level footprint × this number = sloped roof area
  • OSHA classSteep roofOSHA's line is 4/12: at or below is low-slope, above is steep

Nothing you enter leaves your browser. Measure from the attic or a ladder where you can; don't walk a roof to measure it.

Show the math with your numbers
  1. Pitch: 6 ÷ 12 × 12 = 6/12
  2. Angle: arctan(6 ÷ 12) = 26.6°
  3. Multiplier: √(1 + (6 ÷ 12)²) = 1.118
What if: rise per 12 in run
Rise per 12 in runRoof pitch
3 in3/12
4 in4/12
5 in5/12
6 in (yours)6/12
8 in8/12
10 in10/12
12 in12/12

How the calculator works

Three formulas sit behind the results:

  • Pitch: rise ÷ run × 12
  • Angle: arctangent of rise ÷ run
  • Slope multiplier: √(1 + (pitch ÷ 12)²)

For a rise of 6 inches over a run of 12: pitch is 6/12, the angle is 26.6°, the grade is 50%, and the multiplier is 1.118. So 1,000 square feet of level footprint becomes about 1,118 square feet of roof.

Roof pitch chart

Pitch Angle Slope multiplier OSHA class
3/12 14.0° 1.031 Low-slope
4/12 18.4° 1.054 Low-slope
5/12 22.6° 1.083 Steep
6/12 26.6° 1.118 Steep
7/12 30.3° 1.158 Steep
8/12 33.7° 1.202 Steep
9/12 36.9° 1.250 Steep
10/12 39.8° 1.302 Steep
12/12 45.0° 1.414 Steep

What pitch affects

  • Material quantity: steeper roofs have more surface over the same footprint. Use the roof area calculator to work it out.
  • Which materials you can use: the model code limits asphalt shingles to slopes of 2/12 or more. See minimum roof pitch for shingles.
  • Safety: OSHA's rules for workers treat roofs above 4/12 as steep, and fall protection rules apply from 6 feet above a lower level.

Don't have a measurement yet? See how to measure roof pitch.

How much a wrong pitch changes your estimate

Pitch feeds straight into roof area. On 1,000 square feet of footprint, compared with a true 6/12 roof:

You measure Roof area Difference
5/12 1,083 sq ft −3.1%
6/12 1,118 sq ft None
7/12 1,158 sq ft +3.6%
8/12 1,202 sq ft +7.5%

So an error of one step moves area by only a few percent, which your waste allowance can absorb. Being off by two or more steps is worth measuring again.

Frequently asked questions

What does 6/12 mean on a roof?

The roof rises 6 inches for every 12 inches of level distance. That's an angle of about 26.6° and a 50% grade.

How do I convert a roof angle to a pitch?

Multiply the tangent of the angle by 12. For a 30° roof, tan(30°) is 0.577, and 0.577 × 12 gives a pitch of about 6.9/12.

Is 4/12 a steep roof?

Not under OSHA's definition: a slope of 4 in 12 or less is low-slope, and anything greater is steep. That definition applies to workplace rules, and a 4/12 roof can still be dangerous to walk on.

Sources

We use primary sources where we can: building codes, federal rules and manufacturer documents. Read our editorial standards.