Roof Pitch Calculator

This roof pitch calculator converts between rise and run, pitch ratio, angle in degrees, and percent slope. Choose your input mode, enter your values, and read all conversion results at once.

1. Select what you know. Choose "Rise and run" if you measured the vertical and horizontal distances. Use "Pitch ratio" if you know the X/12 value from plans. Choose "Angle" or "Percent slope" to reverse-calculate from an existing measurement.
2. Enter your dimensions. For rise and run mode, use the same unit for both measurements. Mixing inches with feet will produce incorrect results.
3. Add an optional horizontal run length if you want roof height and rafter line length outputs. This is useful for estimating ridge height or rough rafter sizing.
4. Click "Calculate roof pitch" to see the pitch ratio, angle in degrees, percent slope, pitch multiplier, and pitch band classification.
5. Use the pitch multiplier to convert flat plan area into sloped roof surface area. Multiply your footprint square footage by the pitch multiplier for a quick roof area estimate.

This roof pitch calculator also works for shed roofs, lean-tos, and carport overhangs. Enter the known value in any mode and the tool handles all conversions.

Pro tip: always measure horizontal run, not the sloped roof surface. Measuring along the rafters instead of level ground is one of the most common field mistakes and will overstate your pitch result.

Common roof pitch quick reference

Use this table to compare your roof pitch calculator result against common residential pitches.

The roof pitch calculator converts rise and run into every pitch format used in construction. All conversions start from a single slope value.

Slope = Rise / Run. Both measurements must use the same unit. If your rise is 6 inches and run is 12 inches, slope = 6 / 12 = 0.5.

Pitch (X/12) = Slope × 12. A 0.5 slope means 6 inches of rise per 12 inches of run, written as 6/12. This is the standard notation roofers and framers use across the United States.

Angle = atan(Slope) × (180 / π). A 0.5 slope converts to about 26.6 degrees. Use degrees for setting miter saw angles and reading speed square bevels.

Percent slope = Slope × 100. A 0.5 slope is 50%. Percent slope appears on grading plans and site drainage specs more often than X/12 notation.

Pitch multiplier = √(1 + Slope²). For a 6/12 pitch, the multiplier is √(1 + 0.25) = 1.118. Multiply flat footprint area by this factor to estimate the actual sloped roof surface. A 1,000 square foot footprint at 6/12 pitch covers about 1,118 square feet of sloped surface.

Roof pitch calculator worked example

Given: 4 inches of rise over 12 inches of run.

• Slope = 4 / 12 = 0.333
• Pitch = 0.333 × 12 = 4/12
• Angle = atan(0.333) × (180 / π) = 18.4 degrees
• Percent slope = 0.333 × 100 = 33.3%
• Pitch multiplier = √(1 + 0.111) = 1.054

Worked example with horizontal run

Given: 6/12 pitch with a 10 foot horizontal run.

• Slope = 6 / 12 = 0.5
• Roof height = 0.5 × 10 = 5.0 feet
• Pitch multiplier = √(1 + 0.25) = 1.118
• Rafter line length = 10 × 1.118 = 11.18 feet

This rafter line length is the straight diagonal from wall plate to ridge. It does not include overhang, birdsmouth depth, ridge board adjustment, or waste. For complete rafter sizing, use our rafter calculator.

Quick rule

• Pitch = Rise / Run × 12 (same units required)
• Multiply slope by 100 for percent slope
• Multiply footprint area by pitch multiplier for sloped roof area

Common mistakes this calculator helps prevent

Measuring the sloped roof surface instead of the horizontal run is the most common field error. The diagonal is always longer than the run, so using it gives a pitch that's lower than the actual incline.

Using the full building width instead of half the span is another frequent mistake. For a simple gable roof, the run is half the building span. A 30 foot wide building has a 15 foot run, not 30 feet.

Mark both the pitch ratio and the angle on your framing layout. Speed squares use pitch markings (X/12), but miter saws and bevel gauges use degrees. Having both numbers prevents conversion errors on the job site.

Assumptions and limitations

This roof pitch calculator assumes a straight, uniform slope. It does not account for hip rafters, valley rafters, dormers, or compound angles. Rafter line length is the geometric diagonal only and excludes overhang, ridge board thickness, birdsmouth depth, or material waste. For material quantity estimates, use our roofing calculator instead.