Roof Pitch Calculator
Roof pitch is expressed as rise-over-run — how many inches the roof rises for every 12 horizontal inches of run. A 6/12 pitch rises 6 inches per foot, a 12/12 pitch rises at 45 degrees. Pitch affects material quantities (steeper roofs have more surface area), drainage performance (low pitches under 2/12 require special underlayment), and walkability for installation and maintenance. This calculator converts your pitch to degree angle, slope percentage, pitch multiplier (for calculating actual rafter length from horizontal run), and ridge board height above the wall top plate. You can also work backwards from a degree angle. Enter the horizontal rafter run (half the building width) to get the exact rafter length to cut — accounting for pitch but not overhang, which you add separately.
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How to Use This Calculator
- 1Enter your measurements in the fields above. Use the units shown next to each field (ft, in, etc.).
- 2Click Calculate to get your material estimate instantly.
- 3Review the highlighted result — it shows the key quantity you need to order.
- 4Use Copy Results to save your estimate, or bookmark the URL — your inputs are encoded in the link.
Pro tip: Always add 10% to your material order to account for waste, cuts, and defects.
Frequently Asked Questions
What is a good roof pitch?
A 4/12 to 6/12 pitch is considered standard for most residential roofs — gentle enough for safe walking but steep enough for proper water drainage. Asphalt shingles require at least a 2/12 pitch; metal roofing can go as low as 1/12 with standing seam panels.
How do I measure roof pitch without getting on the roof?
Place a level against the roof from the attic, making it horizontal (check the bubble). Measure up 12 inches from one end, then measure from that point straight up to the underside of the roof sheathing. That measurement in inches is your pitch. Example: 6 inches up = 6/12 pitch.
What is the minimum roof pitch for asphalt shingles?
The minimum recommended pitch for standard 3-tab or architectural asphalt shingles is 2/12 (about 9.5 degrees). Below 4/12, you must use double underlayment per NRCA guidelines. Most shingle manufacturers void their warranty below 4/12 unless special low-slope installation methods are followed.
How do I convert roof pitch to degrees?
Use the arctangent formula: degrees = arctan(rise / 12). A 4/12 pitch = arctan(4/12) = 18.4°. A 6/12 pitch = 26.6°. A 12/12 pitch = 45°. The calculator does this conversion automatically for any pitch you enter.