Roof pitch describes vertical rise over horizontal run. A 6:12 roof rises 6 inches for every 12 inches of run, giving a 50% slope and an angle of about 26.57°. Use the chart below to convert x:12 pitch to degrees, slope percentage and a roof-area multiplier.
1. What Does Roof Pitch Mean?
In construction and architectural engineering, roof pitch (also referred to as slope) describes the steepness of a roof plane. In U.S. roofing practice, slope is commonly expressed as units of vertical rise per 12 units of horizontal run.
For example, a 4:12 pitch means that for every 12 horizontal inches you travel toward the ridge, the roof line rises 4 vertical inches. The x:12 notation is common in U.S. roofing; degrees and slope percentage express the same geometry in formats used across markets. Confirm the local drawing and measurement convention for a specific project.
2. Master Pitch, Degree, and Multiplier Table
A pitch multiplier converts a roof plane's horizontal projected area to its sloped area. A complete roof estimate also needs the dimensions of each plane, overhangs, openings, and the chosen material's waste allowance.
| Pitch (x:12) | Angle (degrees) | Slope (%) | Area multiplier |
|---|---|---|---|
| 1:12 | 4.76° | 8.33% | 1.003 |
| 2:12 | 9.46° | 16.67% | 1.014 |
| 3:12 | 14.04° | 25.00% | 1.031 |
| 4:12 | 18.43° | 33.33% | 1.054 |
| 5:12 | 22.62° | 41.67% | 1.083 |
| 6:12 | 26.57° | 50.00% | 1.118 |
| 7:12 | 30.26° | 58.33% | 1.158 |
| 8:12 | 33.69° | 66.67% | 1.202 |
| 9:12 | 36.87° | 75.00% | 1.250 |
| 10:12 | 39.81° | 83.33% | 1.302 |
| 11:12 | 42.51° | 91.67% | 1.357 |
| 12:12 | 45.00° | 100.00% | 1.414 |
Example: A single roof plane with 1,000 ft² of horizontal projected area at 6:12 has 1,000 × √(1 + (6/12)²) = 1118.03 ft² of sloped area. Use the full multiplier in calculations, then round the result; the chart rounds only for display. Material allowance is a separate input.
Measure the projected area of every plane, including any overhangs required by the estimate. The roof pitch and square footage guide explains the area method; the Roofing Material Calculator then converts measured roof area to squares and bundles using your product coverage.
3. Minimum Pitch Requirements by Roofing Material
The 2024 IRC roof assemblies chapter uses vertical units per 12 horizontal units and gives different minimum slopes by roof covering. For example, its asphalt-shingle rules include 2:12 and 4:12 thresholds. A 0:12 slope is mathematically valid, but roofing systems may require positive drainage slope. Check the locally adopted code and the exact product instructions; this guide cannot determine compliance.
Slope suitability depends on the exact roofing product, installation instructions, and local code. The pitch calculation alone cannot establish whether a material is approved for a roof.
As one manufacturer-specific example, GAF's low-slope shingle bulletin describes extra roof-deck protection for many of its shingles on slopes from 2:12 up to, but not including, 4:12. Always check the current instructions for the product you plan to use and confirm local requirements before specifying a roof system.
4. How to Measure Roof Pitch Safely
If an accessible rafter is visible from a safe location, a level and tape measure can provide the rise over a known horizontal run. Do not climb or work at height solely to use this guide; ask a qualified professional when access is unsafe.
- Place an ordinary 12-inch carpenter's level horizontally against the underside of an exposed roof rafter.
- Adjust the level until the air bubble is centered between the indicator lines.
- Measure vertically from the 12-inch mark of the level straight up to the bottom edge of the rafter.
- The number of inches measured is your Rise. If the measurement is 6 inches, your roof has a 6:12 pitch.
Related Roofing Calculators
Use these calculators to estimate slope and material quantities, then verify actual measurements and product requirements:
- Roof Area Calculator — Calculate total square footage and roofing squares accounting for pitch and overhangs.
- Roofing Material Calculator — Estimate roofing squares, bundles, and waste allowance.
Explore related tools in Roofing & Construction.