Roof Pitch Calculator
Convert between roof pitch (rise/run), angle, and slope %. Includes the material area multiplier to estimate true roof area from building footprint.
Reviewed & updated for 2026 by Rakesh Choudhary, PhDMethodology & sources · How we calculate
Roof pitch reference
| Pitch (rise/12) | Angle | Slope % | Multiplier | Category |
|---|---|---|---|---|
| 1/12 | 4.76° | 8.3% | 1.003 | Low slope (special materials) |
| 2/12 | 9.46° | 16.7% | 1.014 | Low conventional |
| 3/12 | 14.04° | 25% | 1.031 | Low conventional |
| 4/12 | 18.43° | 33.3% | 1.054 | Standard residential |
| 6/12 | 26.57° | 50% | 1.118 | Standard residential |
| 8/12 | 33.69° | 66.7% | 1.202 | Steep |
| 9/12 | 36.87° | 75% | 1.250 | Steep |
| 12/12 | 45.00° | 100% | 1.414 | Very steep / dramatic |
| 18/12 | 56.31° | 150% | 1.803 | Very steep / dramatic |
Angles, slopes and multipliers are computed from the rise and run. The category names are this site's plain-English bands, not a code or manufacturer classification.
Why roof pitch matters more than you'd think
Roof pitch isn't just aesthetics, it determines what roofing materials you can use, what the roof will cost to replace, how it handles weather, and whether you can walk on it safely. Every roof covering has a minimum slope set by its manufacturer and by the local building code; below it, water can back up under the laps. Very low slopes are covered with membranes such as EPDM or TPO rather than shingles, and shingles near their minimum often need extra underlayment. Check the product's installation instructions and your local code for the figures.
Steeper pitches take more material, more time and more fall protection to install, and roofers usually price that into labor. Snow slides more readily off a steep roof, while in high-wind regions roof shape and the covering's uplift rating matter as much as pitch.
The area multiplier matters for budgeting. A 2,000 sq ft house footprint at 6/12 pitch needs about 2,236 sq ft of roofing (1.118x multiplier). At 9/12 it's 2,500 sq ft. At 12/12 it's 2,828 sq ft, 41% more material than the footprint itself. Steeper roofs also have proportionally more ridge cap, more flashing, and more vents per linear foot.
Math behind the conversions
Roof pitch in rise/run notation is the tangent of the roof angle. If a roof rises 6 inches per 12 inches of horizontal run, the angle is arctan(6/12) = arctan(0.5) = 26.57°. The slope as a percentage is simply rise/run × 100, so 6/12 is 50% slope. Engineers and road designers prefer slope percentages; carpenters and roofers prefer the rise/run notation.
The area multiplier comes from the Pythagorean theorem. The rafter length (sloped distance) per 12-inch run is √(rise² + 12²). For 6/12: √(36 + 144) = √180 = 13.416. Divide by 12: 13.416/12 = 1.118. That's the multiplier. Conceptually it tells you how much longer the slanted roof surface is compared to the flat horizontal projection.
Common conversions worth memorizing: 4/12 ≈ 18° ≈ 33% slope ≈ 1.054x area. 6/12 ≈ 27° ≈ 50% slope ≈ 1.118x. 9/12 ≈ 37° ≈ 75% slope ≈ 1.25x. 12/12 = 45° = 100% slope = 1.414x (√2). 18/12 ≈ 56° = 150% slope = 1.803x. The relationship is not linear: doubling the rise from 6/12 to 12/12 takes the angle from 26.6° to 45°, less than double, while the slope percentage doubles exactly.
Climate, style and pitch
- Snow: steeper roofs shed snow more readily; a shallow roof must be framed for the snow load your local code sets, and ice dams are a bigger risk.
- Wind: in hurricane regions, local codes set uplift ratings for the covering and its fastening whatever the pitch, and roof shape affects how wind loads the roof.
- Dry climates: where rain is scarce, low-slope roofs with membranes or coatings are common.
- Wet, mild climates: the job is shedding rain rather than snow, so moss and drainage matter as much as steepness.
- Architectural style: Gothic and Victorian roofs tend to be steep, modern designs often low or flat, and the style chosen cascades into material and structural choices.
FAQs
What is roof pitch?
It is how steep a roof is, written as inches of rise per 12 inches of level run. A roof marked 6/12 climbs half a foot over each foot it covers horizontally. The same steepness can be given as an angle (26.57° for 6/12) or a percent grade (50%).
How do I measure roof pitch?
Two methods. (1) Inside an attic: measure horizontally 12 inches along a rafter, then measure vertically up to the roof surface, that vertical is the 'rise' for a 12-inch run. (2) Outside with a level: hold a 12-inch level horizontal against the underside of a roof eave, measure the gap between the level's free end and the rafter, that's the rise.
What is 6/12 pitch in degrees?
About 26.57°. Take the inverse tangent of 6 divided by 12, which is the inverse tangent of 0.5. As a grade it is 50%, because 6 is half of 12.
What's the steepest roof pitch?
Geometry sets no upper limit, and very steep roofs exist on towers and some historic styles. What limits a real roof is the covering: each shingle, tile and panel has a range of slopes its manufacturer supports, sometimes with special fastening at the steep end, and your local building code adds its own rules. Check both before designing around a pitch.
How does pitch affect material needed?
A sloped roof has more surface than the ground it covers, and the pitch multiplier says how much more: 1.054 at 4/12, 1.118 at 6/12, 1.250 at 9/12 and 1.414 at 12/12. So a 1,000 sq ft footprint under a 6/12 roof needs about 1,118 sq ft of roofing, before overhangs and waste.