Roof Pitch Calculator
This roof pitch calculator turns rise and run, a pitch ratio, or an angle into every slope value you need for a roofing project. Enter what you have and instantly read the pitch as x:12, the angle in degrees, the slope percentage, and the multiplier used to size rafters.
It is built for DIY roofers, builders, and estimators who want to check a slope, convert a roof pitch to degrees, or estimate rafter length and roof area before buying materials. Mixed-unit inputs and built-in reference tables keep the math out of your way.
How to Use the Roof Pitch Calculator
Choose your input method
Pick the tab that matches your measurement: Rise & Run to enter the vertical rise and horizontal run, Pitch to type a ratio like 6:12, or Angle to enter the roof angle in degrees (0 to 90).
Enter your values
In Rise & Run mode each field has its own unit selector, so you can mix centimeters, meters, inches, and feet freely. In Pitch mode the run defaults to 12 but can be changed.
Read the six results
Results update as you type: pitch ratio (x:12), angle in degrees, slope percentage, multiplier, rise per 12" run, and rafter length per 12" run. An interactive diagram shows the roof triangle with labeled rise, run, and angle.
Estimate rafter length and area
Once a pitch is calculated, the Rafter & Area Estimator appears. Enter the building span, length, and an optional overhang to get the actual rafter length and total roof area in both metric and imperial units.
Features
Three Input Methods
Calculate from Rise & Run, a Pitch ratio (x:12), or an Angle in degrees, whichever measurement you have on hand.
Mixed Unit Conversion
Rise and run each have their own unit selector for cm, m, inches, or feet, and the conversion is handled automatically.
Interactive Roof Diagram
A live SVG diagram draws the roof as a right triangle with labeled rise, run, angle, and pitch that update as you change inputs.
Six Slope Values
Get pitch ratio, angle, percentage, multiplier, rise per 12" run, and rafter length per 12" run in one result panel.
Rafter & Area Estimator
Enter building span, length, and an optional overhang to estimate actual rafter length and total roof area in metric and imperial.
Common Pitches Table
A reference table covers 1:12 through 12:12 with angle, percentage, multiplier, and a slope category from Low to Very Steep.
Minimum Pitch by Material
Check minimum pitch requirements for nine roofing materials, including asphalt shingles, metal, clay tiles, slate, and membranes.
Real-Time Calculation
Every value recalculates instantly as you type or switch tabs, with no calculate button to press.
Dark Mode Ready
A built-in dark theme keeps the calculator, diagram, and tables comfortable to read in any lighting.
Frequently Asked Questions
How do I calculate roof pitch?
Measure the vertical rise and the horizontal run of the roof, then enter both in the Rise & Run tab. The calculator divides rise by run and scales it to a 12" run, giving you the pitch as x:12 along with the angle, percentage, and multiplier.
What is a 6:12 roof pitch in degrees?
A 6:12 pitch equals about 26.57° and a 50% slope. It is considered a standard residential pitch and works with most roofing materials. Enter 6 and 12 in the Pitch tab to confirm it.
How do I convert roof pitch to degrees?
The angle is the arctangent of rise divided by run. Type any pitch ratio in the Pitch tab and the calculator shows the matching angle automatically. You can also work backward by entering the angle in the Angle tab to get the x:12 pitch.
What does the roof pitch multiplier mean?
The multiplier converts a horizontal measurement into the actual sloped roof surface. A 6:12 pitch has a multiplier of about 1.118, so the roof surface is roughly 11.8% larger than the flat footprint below it. The estimator uses this factor to size rafters and area accurately.
Can I use different units for rise and run?
Yes. In the Rise & Run tab each input has its own unit selector, so you can enter rise in centimeters and run in meters, or any mix of cm, m, inches, and feet. Everything is converted before the pitch is calculated.
What is the minimum pitch for asphalt shingles?
Asphalt shingles need a minimum pitch of 2:12 (about 9.46°). Below that, water may not drain fast enough and can cause leaks. The Minimum Pitch by Material table lists the requirements for nine common materials.
What is a good roof pitch for a house?
Most homes use a pitch between 4:12 and 9:12, with 6:12 a common standard. Steeper roofs shed water and snow better but use more material and labor. Use the Common Pitches table to see where your slope falls and the material table to confirm it suits your roofing.
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