Roof Pitch Calculator
Calculate roof pitch, slope angle in degrees, and slope percentage from vertical rise and horizontal run.
Calculation Results
The vertical rise (in inches) per 12 inches of horizontal run.
The angle of the roof slope relative to the horizontal plane.
The steepness of the roof expressed as a percentage.
How This Calculator Works
To use the Roof Pitch Calculator:
- Enter the vertical rise (the vertical height of the roof span).
- Enter the horizontal run (the horizontal distance over which the rise occurs).
- Select the measurement units (inches, feet, meters, etc.) for both inputs. The calculator converts them to a common base automatically.
- The calculator immediately determines the Pitch Ratio (per 12 units), Slope Angle in Degrees, and Slope Percentage.
Formula & Calculations
Roof pitch is typically expressed as a ratio of vertical rise to horizontal run. In the US, it is traditionally written as rise (in inches) over a standard run of 12 inches:
Pitch Ratio = (Rise / Run) × 12
To convert this slope to an angle in degrees, we use the inverse tangent (arctangent) function:
Roof Angle (Degrees) = arctan(Rise / Run) × (180 / π)
To express the slope as a percentage, we calculate the ratio and multiply by 100:
Slope Percentage = (Rise / Run) × 100
Step-by-Step Calculation Examples
Standard 4/12 Pitch
Calculating the pitch and angle for a standard roof that rises 4 inches for every 12 inches of run.
- rise: 4
- run: 12
- pitch_ratio: 4.0
- roof_angle: 18.4
- slope_percentage: 33.3
Steep 8/12 Pitch
Calculating the pitch and angle for a roof that rises 8 inches for every 12 inches of run.
- rise: 8
- run: 12
- pitch_ratio: 8.0
- roof_angle: 33.7
- slope_percentage: 66.7
Frequently Asked Questions
What does a 4/12 roof pitch mean?
A 4/12 roof pitch means that the roof rises vertically by 4 inches for every 12 inches of horizontal run. It equates to an angle of approximately 18.4 degrees and a slope of 33.3%.
How do I measure roof pitch?
You can measure roof pitch from inside the attic by placing a level horizontally against a rafter, measuring exactly 12 inches along the level, and then measuring the vertical distance from the level to the rafter at that 12-inch point.
What is the standard pitch for residential roofs?
Standard residential roof pitches typically range from 4/12 to 9/12. Roofs with a pitch below 4/12 are considered low slope, while those above 9/12 are steep slope.
What is the minimum pitch for shingles?
The absolute minimum pitch for standard asphalt shingles is 2/12, which requires double underlayment. For standard installation, a pitch of 4/12 or higher is recommended.
How do I convert degrees to roof pitch?
To convert degrees to pitch, take the tangent of the angle in degrees and multiply by 12. For example, tan(18.4°) × 12 ≈ 4. Thus, an 18.4-degree angle is a 4/12 pitch.