Wondering how steep your roof is? Enter rise and horizontal run, and the calculator returns the roof pitch, angle, slope percentage, area multiplier, and slope length in one pass.
Example values — replace these with your measurements.
Quick Presets
Only know an angle or slope percentage? Use the pitch converter.
Pitch, angle, and slope percent describe the same incline on one roof plane. The multiplier and slope length are geometry for that plane. Use them to check the number you just got, not to order materials or decide the roof is safe to walk.
The area multiplier converts horizontal plan area to the sloped surface area of one roof plane.
It does not account for roof shape, overhangs, openings, waste, product coverage, or the final field measurement. Do not treat it as a purchase quantity or final roof area.
In 2021 IRC R905.2.2, asphalt shingles are allowed on slopes of 2:12 or greater. From 2:12 up to 4:12, the model code requires double underlayment.
This is a model-code example, checked July 23, 2026. Your local adopted edition, amendments, and the manufacturer's installation instructions control the work.
Source: 2021 IRC R905.2.2
Pitch alone cannot determine whether a roof is safe to enter or work on. Site conditions, weather, roof condition, edges, access, and the planned work all matter.
For covered construction work, OSHA uses 4:12 or less as low-slope and greater than 4:12 as steep; its roof fall-protection rules include 6-foot unprotected-edge conditions. These classifications do not make a roof safe to walk.
Sources: OSHA 1926.500 definitions and OSHA 1926.501 fall-protection duty
For a framing estimate, use the Rafter Length Calculator . For low-slope drainage questions, use the Flat Roof Slope Calculator .
Follow one set of measurements from the inputs to the five results shown by the calculator.
Divide 6 by 12 to get 0.5, then multiply by 12. The result is a 6:12 pitch. Pitch is a ratio, so 50 centimeters of rise over 100 centimeters of horizontal run gives the same answer.
6:12 pitch is not 30 degrees. The angle is arctan(6 divided by 12), or 26.57 degrees above horizontal. The slope percentage is (6 divided by 12) times 100, or 50%. All three describe the same incline.
The area multiplier is 1.118. For a roof plane with 600 square feet of horizontal plan area, 600 × 1.118 ≈ 671 square feet of sloped surface. Overhangs, openings, and waste are not included. The 6 by 12 triangle has a slope length of 13.42 inches, which describes this triangle, not a framing-ready rafter.
You only need two measurements from the same roof plane.
A correct input matters more than extra decimal places. Use a safe method that gives you a level run.
Compare six common pitches by angle, slope percentage, and area multiplier. Select a row to load it into the calculator.
View the full roof pitch chart
| Pitch | Angle | Slope % | Multiplier | Action |
|---|---|---|---|---|
| 2 : 12 | 9.5° | 16.7% | 1.014 | |
| 3 : 12 | 14.0° | 25.0% | 1.031 | |
| 4 : 12 | 18.4° | 33.3% | 1.054 | |
| 6 : 12 | 26.6° | 50.0% | 1.118 | |
| 8 : 12 | 33.7° | 66.7% | 1.202 | |
| 12 : 12 | 45.0° | 100.0% | 1.414 |
3:12 is a 25% slope. 12:12 is 45 degrees. The area multiplier is √(1 + (pitch/12)²). Use it for a rough area check, not an order quantity.
Stay here when you have rise and horizontal run. Leave when your starting values or the next job are different.
| Known information | Use this page | Why |
|---|---|---|
| Rise and horizontal run | Roof Slope Calculator | Calculate the roof pitch and supporting geometry. |
| Angle, percentage, or 1:N ratio | Pitch Converter | Convert between pitch formats without measuring rise and run. |
| Span, overhang, or ridge deduction | Rafter Length Calculator | Include framing details that a slope-only result cannot know. |
| Low-slope drainage questions | Flat Roof Slope Calculator | Check fall, ponding, and low-slope material limits. |
| Need to find rise and run first | How to Measure Roof Pitch | Get a level run from the attic, ground, or a phone without guessing. |
| Want the full pitch table | Roof Pitch Chart | Look up angle, slope percent, and multiplier for pitches 1:12 to 24:12. |
| Two wall heights or a lean-to span | Lean-to Roof Pitch Calculator | Solve wall height, pitch, or slope length on a single-slope lean-to. |
Divide the rise by the horizontal run. Multiply that value by 12 for an X:12 pitch or by 100 for slope percentage. To find the angle, convert arctan(rise / run) to degrees. For example, a 6-inch rise over a 12-inch run is a 6:12 pitch, a 50% slope, and about 26.6 degrees.
They describe the same roof steepness in different formats. Pitch shows rise per 12 units of horizontal run, such as 6:12. Angle measures degrees above horizontal. Slope percentage is rise divided by run, multiplied by 100. A 12:12 pitch is 45 degrees. A 3:12 pitch is a 25% slope. A 6:12 pitch is 50%, not 30 degrees.
Yes. Convert the angle or slope percentage to an equivalent X:12 pitch. Use the dedicated converter when rise and horizontal run are not your starting values. Convert pitch, angle, or slope.
There is no single standard pitch. In the US, most conventional homes use pitches between 4:12 and 9:12, chosen for drainage, climate, style, and roofing material. Roofs below 4:12 are usually treated as low-slope systems with stricter material requirements.
There is no single minimum for every roof. The lowest allowed slope depends on the roofing system, the manufacturer's installation instructions, and the locally adopted code. Shingles, metal panels, and low-slope membranes each have their own limits, and going below them risks ponding and premature failure. See low-slope roofing system requirements.
Asphalt shingles have a minimum application slope, and roofs near that minimum usually need extra installation steps such as reinforced underlayment. Whether a specific slope qualifies depends on the shingle manufacturer's instructions and the locally adopted code, not on the geometry alone. Compare low-slope roofing systems.
Pitch alone cannot determine whether a roof is safe to enter. OSHA classifies roofs of 4:12 or less as low-slope and steeper as steep for its construction fall-protection rules, but site conditions, weather, roof condition, edges, and access all matter. Treat any roof access as requiring a safe plan.
There is no universal threshold. Around 30 degrees (about 7:12) is often cited as the point where snow sheds more readily, but results depend on material, temperature, wind, and exposure. Steeper pitches generally retain less snow, while low-slope roofs may need design for snow load and drainage.
Measure each roof plane separately. Calculate each slope on its own, then use the appropriate roof-area or framing tool for the geometry you are planning.
This tool is built and maintained by an independent developer. The math is standard rise/run geometry, and automated tests cover normal inputs plus edge cases like very small runs. Where practical, the code and safety sources are linked so you can check them.
Results describe roof-plane geometry. They do not replace a site measurement, structural design, local code review, or manufacturer installation instructions.
Method and source notes last reviewed July 2026.