How to Find Your Roof Pitch
Measure the pitch as the rise, in inches, over a level run of 1 ft: a level and a tape on the roof or against a rafter in the attic give it directly, and an angle reading converts to it in the tables below.
Estimates for planning, not professional advice. Read the full notice.
Work it out for your own sizes
Turn your rise and run into a pitchExample to try: Rise 6 in, Run 1 ft
Local codes and amendments differ; your building department decides.
Step by step
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Step 1: On the roof: level and tape
Rest one end of the level on the roof surface and raise the other end until the bubble sits in the middle. Mark 1 ft along the level from the end on the roof, then measure straight down from the level to the roof at that mark. That distance in inches is the first number of the pitch: the roof rises that many inches in twelve.
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Step 2: From the attic: level against a rafter
Hold the level horizontal with one end touching the underside of a rafter. Mark 1 ft along the level, then measure straight up from the level to the rafter at that mark. The distance in inches is the rise in twelve, the same reading as on the roof.
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Step 3: From an angle reading
An angle finder or a phone level reads the slope in degrees. Find the angle in the second table, or enter it in the roof pitch calculator, which converts degrees to a pitch.
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Step 4: Read it against a longer level
With a longer level, measure the rise over its whole length and look it up in the first table: it gives the same slope as a rise in twelve, with the angle, percent and area factor.
A reading over a longer level, halved to the pitch
Rise read over a level of one length, the same slope as a rise in twelve, its angle, percent and area factor
| Rise read over a 24 in level | Same slope as a rise in 12 | Angle | Percent slope | Area factor |
|---|---|---|---|---|
| 6 in | 3 in 12 | 14.04 degrees | 25 percent | 1.031 |
| 8 in | 4 in 12 | 18.43 degrees | 33.33 percent | 1.054 |
| 1 ft | 6 in 12 | 26.57 degrees | 50 percent | 1.118 |
| 1 ft 4 in | 8 in 12 | 33.69 degrees | 66.67 percent | 1.202 |
| 1 ft 8 in | 10 in 12 | 39.81 degrees | 83.33 percent | 1.302 |
| 2 ft | 12 in 12 | 45 degrees | 100 percent | 1.414 |
Estimate for planning, from what you entered and the product data shown. Check product labels and your supplier before you buy.
A longer level gives a bigger reading for the same roof: read the rise over the level's whole length, then the pitch is that rise scaled to twelve inches of run. The area factor turns a flat area into the area of the sloped surface.
An angle reading as a pitch
The pitch, percent slope and area factor for each angle read in degrees
| Angle read | Pitch | Percent slope | Area factor |
|---|---|---|---|
| 10 degrees | 2.12 in 12 | 17.63 percent | 1.015 |
| 15 degrees | 3.22 in 12 | 26.79 percent | 1.035 |
| 20 degrees | 4.37 in 12 | 36.4 percent | 1.064 |
| 25 degrees | 5.6 in 12 | 46.63 percent | 1.103 |
| 30 degrees | 6.93 in 12 | 57.74 percent | 1.155 |
| 35 degrees | 8.4 in 12 | 70.02 percent | 1.221 |
Pitch is the tangent of the angle times twelve; the pitch calculator takes degrees directly.
What the x-in-12 number means
The roof trade writes pitch as a rise over twelve units of run, and the 2021 IRC writes slopes the same way. Its wording for asphalt shingles, where the notation shows:
Asphalt shingles shall be used only on roof slopes of 2 units vertical in 12 units horizontal (17-percent slope) or greater. For roof slopes from 2 units vertical in 12 units horizontal … up to 4 units vertical in 12 units horizontal (33-percent slope), double underlayment application is required…
The roof pitch chart lists every whole pitch with its angle and percent.
Questions
How do I measure roof pitch from the ground or the attic?
From the attic, hold a level against the underside of a rafter and measure the rise at the one-foot mark, as in the second step. The three ways on this page work at the roof, against a rafter, or from an angle reading; the pitch calculator converts any of them.
What is a 4/12 pitch?
A roof that rises four inches for every twelve inches of run. Enter that rise and a twelve inch run in the pitch calculator to see its angle, percent slope and area factor.
How do I turn an angle into a pitch?
Look the angle up in the second table, or enter degrees in the pitch calculator. Both use the same engine: the rise in twelve is twelve times the tangent of the angle.
What pitch is my roof if it rises a given amount?
Measure the rise over a known level run and enter both in the pitch calculator: it scales them to a rise in twelve and gives the angle, percent and area factor with the working shown.
Calculate it for your project
Enter your own sizes to get the amount to buy or the layout figures, with the working shown and a page to print.
Check your reading in the pitch calculatorSources (1)
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2021 IRC, Chapter 9 Roof Assemblies, R905.2.2 Slope (opens in new tab), International Code Council, 2021 IRC.
Code or government.
“Asphalt shingles shall be used only on roof slopes of 2 units vertical in 12 units horizontal (17-percent slope) or greater. For roof slopes from 2 units vertical in 12 units horizontal … up to 4 units vertical in 12 units horizontal (33-percent slope), double underlayment application is required…”
Checked November 12, 2026. Figures and codes change; verify with the source. Back to where this is used (Source 1)
These are summaries of what the sources say, not professional advice. Codes and product data change. Check with your building department and the product label about your own project.