Enter your roof's Rise and Run measurements into the Roof Pitch Calculator to find your Pitch Ratio, Roof Angle, and Rafter Length — plus add a Rafter Overhang value and choose your preferred Measurement Unit to get the full picture, including Slope Percentage and Pitch (Decimal).
Pitch Ratio
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Pitch (Decimal)
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Roof Angle
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Rafter Length
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Slope Percentage
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Rise
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Run
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Roof pitch is the slope or steepness of a roof, typically expressed as a ratio like 4:12, meaning the roof rises 4 units for every 12 units of horizontal run. It can also be expressed as an angle in degrees or as a percentage.
To calculate roof pitch, divide the rise by the run. For example, if your roof rises 4 feet over a 12-foot run, the pitch is 4/12 or 1/3. This is commonly written as 4:12 pitch.
The most common roof pitches range from 4:12 to 9:12. A 6:12 pitch (26.57° angle) is considered standard for many residential homes as it provides good water drainage while being practical to build and maintain.
A 4/12 roof pitch means the roof rises 4 units vertically for every 12 units horizontally. This creates an angle of approximately 18.43 degrees and is considered a moderate slope that's suitable for most roofing materials.
For areas with heavy snow loads, a minimum pitch of 6:12 (26.57°) is recommended to ensure proper snow shedding. Steeper pitches like 8:12 or 9:12 are even better for preventing snow accumulation.
The best roof pitch depends on your climate, roofing material, and architectural style. Generally, 6:12 to 8:12 pitches work well for most situations, providing good drainage, snow shedding, and structural efficiency.
Rafter length is calculated using the Pythagorean theorem: rafter² = rise² + run². Take the square root of the sum to get the rafter length. Don't forget to add any overhang length to the total.
Pitch is typically expressed as a ratio (like 4:12), while slope can be expressed as a percentage, decimal, or angle. Both describe the steepness of the roof but use different units of measurement.