Roof Slope Calculator
Calculate roof slope, roof pitch, roof angle, rise, run, and rafter length from your measurements.
Enter Your Measurements
Roof Slope Results
Roof slope is calculated by comparing the vertical rise with the horizontal run.
How to Use the Roof Slope Calculator
Our free roof slope calculator helps you calculate roof slope, roof pitch, roof angle, rise, run, and rafter length from your roof measurements. Enter the vertical rise and horizontal run, select the appropriate units, and calculate the results instantly.
- Enter the vertical rise of the roof.
- Enter the horizontal run of the roof.
- Select the unit for each measurement.
- Click Calculate Roof Slope.
- Review the calculated slope, pitch, angle, and rafter length.
What Is Roof Slope?
Roof slope describes the relationship between the vertical rise and horizontal run of a roof. It is commonly expressed as a percentage or as a ratio showing how much the roof rises compared with its horizontal distance.
For example, a roof that rises 6 units for every 12 units of horizontal run has a slope of 50%. The same roof can also be described as having a 6:12 roof pitch.
Roof Slope Formula
Roof slope can be calculated by dividing the vertical rise by the horizontal run and multiplying the result by 100.
Roof Slope (%) = (Rise ÷ Run) × 100
For example, if the rise is 6 feet and the run is 12 feet:
(6 ÷ 12) × 100 = 50%
Therefore, a roof with a 6-foot rise and a 12-foot run has a roof slope of 50%.
What Does This Roof Slope Calculator Calculate?
This calculator provides several related roof measurements based on the rise and run you enter.
- Roof Slope: The roof slope expressed as a percentage.
- Roof Pitch: The amount of rise for every 12 inches of horizontal run.
- Roof Angle: The angle of the roof measured from the horizontal.
- Rise: The vertical measurement entered for the roof.
- Run: The horizontal measurement entered for the roof.
- Rafter Length: The diagonal distance calculated from the rise and run.
Roof Slope Example
Suppose a roof has a vertical rise of 6 feet and a horizontal run of 12 feet.
Using the roof slope formula:
(6 ÷ 12) × 100 = 50%
The roof therefore has a slope of 50%. The same measurements correspond to a 6:12 roof pitch and a roof angle of approximately 26.57 degrees.
The calculated rafter length for these measurements is approximately 13 feet 5 inches.
Roof Slope vs. Roof Pitch
Roof slope and roof pitch describe the same basic rise-and-run relationship, but they are normally expressed differently.
Roof slope is commonly expressed as a percentage. Roof pitch is commonly expressed as a ratio such as 6:12, meaning the roof rises 6 inches for every 12 inches of horizontal run.
For example, a 6:12 roof pitch corresponds to a 50% roof slope.
Common Roof Slope and Pitch Values
Different buildings can use different roof slopes depending on design, drainage, roofing materials, climate, and construction requirements.
- 2:12 — approximately 16.67% slope
- 3:12 — 25% slope
- 4:12 — approximately 33.33% slope
- 5:12 — approximately 41.67% slope
- 6:12 — 50% slope
- 8:12 — approximately 66.67% slope
- 10:12 — approximately 83.33% slope
- 12:12 — 100% slope
How Roof Slope Affects Rafter Length
Roof slope affects rafter length because the slope determines the vertical rise for a given horizontal run.
When the horizontal run remains the same, increasing the roof slope increases the rise. This produces a longer diagonal rafter.
A lower roof slope produces a smaller rise and therefore a shorter rafter for the same horizontal run.
If you need additional rafter measurements, use our Rafter Calculator.
Roof Slope Measurements and Units
This roof slope calculator allows you to enter rise and run using feet, inches, meters, or centimeters.
The rise and run should describe the same section of the roof. Accurate measurements are important because the calculated slope, pitch, angle, and rafter length depend directly on the values entered.
Frequently Asked Questions
How do you calculate roof slope?
Divide the vertical rise by the horizontal run and multiply the result by 100. The result is the roof slope expressed as a percentage.
What is a 6:12 roof slope?
A 6:12 roof pitch means the roof rises 6 inches for every 12 inches of horizontal run. This corresponds to a 50% roof slope.
What is the difference between roof slope and roof pitch?
Roof slope is commonly expressed as a percentage, while roof pitch is commonly expressed as a rise-over-12 ratio. For example, a 6:12 pitch equals a 50% slope.
Does roof slope affect rafter length?
Yes. For the same horizontal run, a steeper roof slope creates a greater vertical rise and therefore a longer rafter.
Can I calculate roof angle from roof slope?
Yes. Roof slope and roof angle are mathematically related. This calculator calculates the roof angle from the rise and run you enter.
Important Information
The results provided by this calculator are mathematical estimates based on the measurements entered by the user. Actual roof construction can involve additional factors such as framing methods, structural loads, lumber dimensions, roofing materials, local building codes, and design requirements.
Always verify measurements and construction requirements before using calculator results for actual building work. Consult applicable building codes and a qualified professional when structural decisions are involved.
Related Calculators
Explore our other roofing calculators to calculate rafter dimensions, roof pitch, and roof angle.
Calculate Your Roof Slope
Enter your roof rise and run above to calculate roof slope, roof pitch, roof angle, and rafter length.