Roof Pitch Calculator
Reviewed by the My Roof Pitch editorial team · Updated · Free, no sign-up, works offline after first load
Roof pitch is the ratio of vertical rise to horizontal run, written as X:12. A 6:12 pitch rises 6 inches over 12 inches of run, equal to 26.57° or a 50% slope. Divide rise by run, then apply arctangent to get the angle in degrees.
Key takeaways
- Roof pitch is written rise:12 in the US — a 6:12 roof rises 6 inches for every 12 inches of horizontal run.
- Pitch in degrees = arctan(rise ÷ run). 4:12 is 18.43°, 6:12 is 26.57°, 12:12 is exactly 45°.
- The pitch multiplier √(rise² + run²) ÷ run converts a flat footprint into true sloped roof area.
- Asphalt shingles need 2:12 minimum with double underlayment, 4:12 for standard installation (2021 IRC R905.2.2).
- Roofs up to about 6:12 are generally walkable; above 9:12 crews need staging or a rope system.
Pitch Studio
Pick what you know and enter the values.
The classic field measurement: rise over a horizontal run.
Vertical height gained.
Horizontal distance the rise happens over.
Advanced options
Horizontal projection past the wall. Added along the slope.
Half of this is deducted from the run — the reason DIY rafters come out long.
Analysis
Live results from your measurements.
≈ 6 in per 12 in
Walkable with care. Most crews still use roof jacks and a harness.
Partial snow shedding. Ice dams remain possible at eaves without good ventilation and an ice-and-water barrier.
Well above minimum drainage slope; water clears quickly.
Which roofing materials are approved at 6:12?
- Asphalt shingles (standard) (min 4:12, IRC R905.2.2)
- Asphalt shingles (double underlayment) (min 2:12, IRC R905.2.2 exception)
- Standing seam metal (min 0.25:12, IRC R905.10.1.1, 1/4:12)
- Corrugated / exposed-fastener metal (min 3:12, IRC R905.10.1.1)
- Clay or concrete tile (min 2.5:12, IRC R905.3.1)
- Slate (min 4:12, IRC R905.6.1)
- Wood shingles (min 3:12, IRC R905.7.1)
- Wood shakes (min 4:12, IRC R905.8.6)
- EPDM / TPO / PVC membrane (min 0.25:12, IRC R905.11–R905.13)
- Modified bitumen (min 0.25:12, IRC R905.11)
Minimums follow the 2021 IRC Chapter 9. Manufacturers may require a steeper minimum.
Show the working
- Slope ratio:
rise ÷ run= 0.5 - Pitch:
0.5 × 12= 6:12 - Angle:
arctan(0.5)= 26.57° - Multiplier:
√(0.5² + 1)= 1.118
Carries your pitch, multiplier and (if enabled) sloped area across.
What this calculator does
Roof pitch describes how steep a roof is. In the United States it is written as a ratio of vertical rise to a fixed 12 units of horizontal run — a 6:12 roof climbs 6 inches for every 12 inches you move sideways. Everywhere else the same steepness is usually given as an angle in degrees, or as a percentage grade. All three describe one number: the tangent of the roof angle. Pitch drives almost every other roofing decision. It sets which materials are approved, how much surface area you actually have to cover, how much snow the roof sheds, whether a crew can walk it, and how long the rafters need to be.
How to use it
- Set a level horizontally against the underside of a rafter or against the roof surface, with one end touching the roof.
- Measure 12 inches along the level from the point where it touches the roof and mark it.
- Measure straight up or down from that 12-inch mark to the roof surface. That vertical distance is your rise.
- Enter the rise and the 12-inch run into the calculator above.
- Read the pitch as a ratio, the angle in degrees and the slope percentage from the results panel.
The formula
Pitch ratio
pitch = rise / run, expressed per 12 units of run
Divide rise by run, then multiply by 12 to state the result in the standard X:12 form used on framing plans.
Angle in degrees
angle = arctan(rise / run) × (180 / π)
The roof is a right triangle. The angle at the eaves is the arctangent of rise over run, converted from radians to degrees.
Pitch multiplier
multiplier = sqrt(rise^2 + run^2) / run
Multiply a flat footprint area by this number to get true sloped roof area. A 6:12 roof has a multiplier of 1.1180, so its surface is 11.8% larger than its footprint.
Worked example
A level held against a rafter shows 7 inches of rise across a 12-inch run.
- Ratio: 7 ÷ 12 = 0.5833
- Pitch: 0.5833 × 12 = 7:12
- Angle: arctan(0.5833) = 30.26°
- Slope: 0.5833 × 100 = 58.3%
- Multiplier: √(7² + 12²) ÷ 12 = 13.892 ÷ 12 = 1.1577
A 7:12 roof sits at 30.26°, a 58.3% slope, and its surface area is 15.77% larger than the footprint below it.
Reference chart
| Pitch (rise:12) | Angle (degrees) | Slope (%) | Pitch multiplier |
|---|---|---|---|
| 1:12 | 4.76 | 8.3 | 1.0035 |
| 2:12 | 9.46 | 16.7 | 1.0138 |
| 3:12 | 14.04 | 25 | 1.0308 |
| 4:12 | 18.43 | 33.3 | 1.0541 |
| 5:12 | 22.62 | 41.7 | 1.0833 |
| 6:12 | 26.57 | 50 | 1.118 |
| 7:12 | 30.26 | 58.3 | 1.1577 |
| 8:12 | 33.69 | 66.7 | 1.2019 |
| 9:12 | 36.87 | 75 | 1.25 |
| 10:12 | 39.81 | 83.3 | 1.3017 |
| 11:12 | 42.51 | 91.7 | 1.3566 |
| 12:12 | 45 | 100 | 1.4142 |
| 14:12 | 49.4 | 116.7 | 1.5366 |
| 16:12 | 53.13 | 133.3 | 1.6667 |
| 18:12 | 56.31 | 150 | 1.8028 |
| 24:12 | 63.43 | 200 | 2.2361 |
Minimum roof pitch by roofing material
| Material | Minimum pitch | Code reference |
|---|---|---|
| Asphalt shingles (standard) | 4:12 | IRC R905.2.2 |
| Asphalt shingles (double underlayment) | 2:12 | IRC R905.2.2 exception |
| Standing seam metal | 0.25:12 | IRC R905.10.1.1, 1/4:12 |
| Corrugated / exposed-fastener metal | 3:12 | IRC R905.10.1.1 |
| Clay or concrete tile | 2.5:12 | IRC R905.3.1 |
| Slate | 4:12 | IRC R905.6.1 |
| Wood shingles | 3:12 | IRC R905.7.1 |
| Wood shakes | 4:12 | IRC R905.8.6 |
| EPDM / TPO / PVC membrane | 0.25:12 | IRC R905.11–R905.13 |
| Modified bitumen | 0.25:12 | IRC R905.11 |
Common mistakes
- Confusing pitch with slope. Pitch traditionally means rise over the full span; slope means rise over run. Modern usage treats X:12 as slope, and that is what every calculator and code table uses.
- Measuring rise over a run other than 12 and reporting it as X:12 without scaling. A 4-inch rise over an 8-inch run is 6:12, not 4:12.
- Measuring on top of the shingles at an overlap. Thickness variation there can shift the reading by a full inch of rise.
- Using the footprint area for material orders. A pitched roof always has more surface than the building below it.
- Reading a pitch off a sagging or historic rafter and assuming the whole roof matches. Take three readings in different bays.
- Rounding the angle before using it in a trigonometric step. Round only at the very end.
Assumptions and limits
- The roof plane is flat and straight between eave and ridge — no sag, no curvature, no changing pitch.
- Rise and run are measured in the same unit. The calculator converts for you if you switch units.
- Results describe one roof plane. Multi-pitch roofs need one calculation per plane.
- Material minimums quoted come from the 2021 IRC and are a general guide, not a substitute for your local adopted code.
Frequently asked questions
What is a 4/12 roof pitch in degrees?
A 4/12 roof pitch is 18.43 degrees. Divide 4 by 12 to get 0.3333, then take the arctangent of 0.3333. The same roof is a 33.3% slope and has a pitch multiplier of 1.0541.
What is the most common residential roof pitch?
Most US houses fall between 4:12 and 9:12, with 6:12 the single most common. That range sheds water well, keeps attic space usable, and stays inside the limits where standard asphalt shingles and normal framing are approved.
What roof pitch is walkable?
Roofs up to about 6:12 (26.57°) are generally walkable in dry conditions with soft-soled boots. From 7:12 to 9:12 crews use roof jacks. Above 9:12 (36.87°) staging or a rope system is standard practice.
What is the minimum roof pitch for shingles?
Asphalt shingles need at least 2:12 under the IRC, and only with two layers of underlayment. From 4:12 up, a single underlayment layer is allowed. Below 2:12 you need a membrane system rather than shingles.
How do I measure roof pitch without going on the roof?
Measure from inside the attic. Hold a level against the underside of a rafter, mark 12 inches along it, then measure vertically from that mark to the rafter. That vertical distance is your rise over a 12-inch run.
Is roof pitch the same as roof slope?
In strict traditional usage, no — pitch was rise over total span and slope was rise over run. In current building practice and in every code table, both terms mean rise over a 12-unit run, and that is how this calculator treats them.
What is a pitch multiplier used for?
It converts the flat footprint area of a building into the true sloped area of its roof. Multiply the plan-view square footage by the multiplier before ordering shingles, underlayment or sheathing.
How steep is a 12/12 roof?
A 12/12 roof is exactly 45 degrees, a 100% slope, with a pitch multiplier of 1.4142. It cannot be walked safely without fall protection and costs noticeably more to roof because of the access and staging required.
Related guides
- How to Calculate Roof Pitch: 6 Methods That Actually WorkSix field-tested ways to find the pitch of a roof — from the ladder, from the attic, from a photo — plus the arithmetic that turns any measurement into X:12, degrees and percent.
- Roof Pitch to Degrees: Full Conversion Chart and FormulaThe complete pitch-to-degree conversion table, the trigonometry behind it, and why 6:12 is 26.57° rather than the 30° people expect.
- Common Roof Pitches Explained: 3:12 Through 12:12A pitch-by-pitch breakdown of every slope you will meet on a house — what each one costs, what it can be covered with, and which climates it suits.
- Minimum Roof Pitch by Material: IRC Limits for Every CoveringEvery covering has a slope below which water gets under it. Here are the code minimums, the underlayment upgrades that unlock them, and what to use when your roof is too flat.
- Shed and Lean-To Roof Pitch: How to Choose and Calculate ItSingle-slope roofs use the whole building depth as run, which changes every calculation. Here is the geometry, the wall-height math and the pitch to pick for a shed, lean-to or carport.
- Metal Roof Pitch: Minimums, Panel Lengths and Cost by SlopeMetal covers a wider slope range than any other roofing, but only if you match the profile to the pitch. Minimums, panel take-off, weight and the cost curve across slopes.
Last updated 2026-08-05. Results are estimates for planning and are not a substitute for a licensed engineer or local code review.