🏘 Roof Pitch Calculator
Calculate roof pitch (x/12), angle in degrees, slope percentage, and rafter length multipliers.
Angle (Degrees)
Slope (Grade)
Rafter Multiplier
What does Roof Pitch mean?
In carpentry, roof pitch is expressed as a fraction over 12 (e.g., 4/12, 6/12, 8/12). The "12" represents the horizontal run (12 inches or 1 foot). The first number represents the vertical rise (how many inches the roof goes up for every foot it goes across).
A "flat roof" is generally defined as having a pitch between 1/12 and 2/12. A "standard" residential pitched roof is usually between 4/12 and 9/12. Anything over 9/12 is considered a steep roof.
What is the Rafter Multiplier?
The "Rafter Multiplier" (also called the slope factor) is a mathematical constant used to find the exact length of a rafter (the hypotenuse of the triangle) when you only know the horizontal run of the building.
For example, if your house is 20 feet wide (a 10-foot run to the center peak) and your roof pitch is 6/12, the rafter multiplier is 1.118. Therefore, your rafter length is exactly 10 ft × 1.118 = 11.18 feet.