Roof Pitch Calculator
Calculate roof pitch as a ratio, angle in degrees, and slope percentage from rise and run measurements. See also Rafter Length Calculator, Roofing Calculator, and Stair Calculator.
Input Method
Roof Pitch Diagram
How to Use the Roof Pitch Calculator
Enter the rise and run of your roof in inches, or switch to angle mode and enter the roof angle in degrees. The standard convention expresses pitch as rise per 12 inches of run (e.g., 6:12 means the roof rises 6 inches for every 12 inches of horizontal run). The rafter factor tells you how many feet of rafter you need per foot of horizontal run — multiply by the total run to get rafter length.
Formula
Pitch = Rise / Run (expressed as X:12)
Angle = arctan(Rise / Run) x 180 / PI
Slope % = (Rise / Run) x 100
Rafter Factor = sqrt(1 + (Rise/Run)²)
Rafter Length = Run (ft) x Rafter Factor
Example Calculation
Rise = 6 inches, Run = 12 inches
Pitch = 6:12
Angle = arctan(6/12) = 26.57°
Slope = (6/12) x 100 = 50%
Rafter factor = sqrt(1 + 0.25) = 1.1180
For 15 ft run: rafter = 15 x 1.118 = 16.77 ft
Common Roof Pitches Reference
| Pitch | Angle | Slope % | Rafter Factor | Common Use |
|---|---|---|---|---|
| 1:12 | 4.76° | 8.3% | 1.0035 | Flat roof (minimum drainage) |
| 2:12 | 9.46° | 16.7% | 1.0138 | Low slope, rolled roofing |
| 4:12 | 18.43° | 33.3% | 1.0541 | Standard minimum for shingles |
| 6:12 | 26.57° | 50.0% | 1.1180 | Common residential |
| 8:12 | 33.69° | 66.7% | 1.2019 | Steep residential |
| 10:12 | 39.81° | 83.3% | 1.3017 | Very steep, colonial style |
| 12:12 | 45.00° | 100% | 1.4142 | Maximum standard pitch |
Frequently Asked Questions
What is the most common roof pitch?
The most common residential roof pitches are 4:12 to 9:12. A 6:12 pitch (26.57°) is the most popular for standard homes — it provides good water drainage, allows walking on the roof for maintenance, and works with all roofing materials including asphalt shingles.
What is the minimum pitch for shingles?
Asphalt shingles require a minimum 4:12 pitch (some manufacturers allow 2:12 with special underlayment). Metal roofing can go as low as 1:12. Rolled roofing works at 2:12 minimum. Below 2:12, use a membrane roof system (TPO, EPDM, or built-up).
How do I measure roof pitch from inside the attic?
Place a level horizontally against a rafter and mark 12 inches from the rafter. Measure vertically from the 12-inch mark down to the level — this measurement in inches is your pitch per 12. For example, if you measure 6 inches, your roof is 6:12.
How does roof pitch affect material cost?
Steeper roofs require more material because the roof surface area increases. A 12:12 pitch has 41% more surface area than a flat roof of the same footprint. Labor costs also increase for pitches above 6:12 due to safety equipment requirements and slower work pace.
What pitch is considered a "walkable" roof?
Roofs with a pitch of 6:12 or less are generally considered walkable without special equipment. Pitches of 7:12 to 9:12 require roof jacks or toe boards. Above 9:12, scaffolding or harness systems are necessary for safe access.
Does roof pitch affect snow load?
Yes. Steeper roofs shed snow more effectively. Roofs below 3:12 in snowy climates must be designed for full ground snow load. At 6:12, snow load is reduced by about 30%. Above 7:12, most snow slides off naturally, but ice dams can still form at eaves.