Convert rise & run to pitch ratio, angle, slope percentage, and rafter multiplier — instantly.
Roof pitch is the measure of a roof's steepness, expressed as a ratio of vertical rise to horizontal run. In the United States, pitch is almost universally written as X/12 — meaning the roof rises X inches for every 12 inches of horizontal distance. A 6/12 pitch rises 6 inches for every foot of run, while a 12/12 pitch rises at a perfect 45-degree angle.
Pitch affects everything from drainage performance and material selection to labor costs and attic space. Steeper roofs shed water and snow faster, provide more attic headroom, and offer stronger curb appeal — but they cost more to build and are harder to walk safely. Low-slope roofs are cheaper and easier to install but require special waterproofing materials and more diligent maintenance.
Beyond the X/12 notation, roof slope can also be expressed as a decimal ratio (rise ÷ run), a degree angle, or a slope percentage. Our calculator converts between all of these automatically, and also outputs the rafter length multiplier — a handy factor you multiply by the run to get true rafter length before adding overhangs.
You can measure roof pitch from the outside, from a ladder, or from inside the attic — no need to climb to the peak.
Rest a 24-inch level horizontally against the roof surface. Hold one end touching the roof, keep the bubble centered, then measure straight down from the 12-inch mark on the level to the roof surface. That vertical measurement in inches is your rise; your pitch is rise/12.
Hold a level against the underside of a rafter, make it perfectly level, and mark the 12-inch point. Measure straight down from that mark to the rafter. This vertical distance is your rise. This method is especially useful during winter or on steep roofs where exterior access is difficult.
A speed square has a built-in pitch scale. Hold the pivot point against the rafter and rotate the square until the level vial reads level. Read the degree or common-pitch scale directly — it's the fastest method for framers already on the roof.
Use this reference table to quickly look up common pitches and their equivalent angle, slope percentage, and rafter multiplier.
| Pitch | Angle | Slope % | Multiplier | Category |
|---|---|---|---|---|
| 2/12 | 9.46° | 16.7% | 1.0138 | Low slope |
| 3/12 | 14.04° | 25.0% | 1.0308 | Low slope |
| 4/12 | 18.43° | 33.3% | 1.0541 | Conventional |
| 5/12 | 22.62° | 41.7% | 1.0833 | Conventional |
| 6/12 | 26.57° | 50.0% | 1.1180 | Conventional |
| 7/12 | 30.26° | 58.3% | 1.1577 | Conventional |
| 8/12 | 33.69° | 66.7% | 1.2019 | Steep |
| 9/12 | 36.87° | 75.0% | 1.2500 | Steep |
| 10/12 | 39.81° | 83.3% | 1.3017 | Steep |
| 11/12 | 42.51° | 91.7% | 1.3566 | Steep |
| 12/12 | 45.00° | 100.0% | 1.4142 | Steep |
While any pitch from 1/12 to 24/12 is technically possible, a handful of pitches dominate residential construction:
For most residential homes, a pitch between 4/12 and 6/12 is considered ideal. These pitches drain effectively in rain and snow, are compatible with every major shingle type, and allow roofers to work safely without harnesses in most jurisdictions. Anything above 6/12 still performs well but costs more — plan for a 10–20% labor premium from most contractors. Below 4/12, you'll need to verify your chosen shingle manufacturer's warranty requirements for low-slope applications.
Most asphalt shingle manufacturers set a minimum pitch of 2/12 (approximately 9.5°), but only when installed with a double layer of underlayment and, in many cases, an ice-and-water shield across the entire deck. The practical standard minimum is 4/12 for a normal single-layer installation under most building codes. At 2/12–3/12, water moves slowly enough that capillary action can push moisture under shingle tabs; the extra underlayment compensates for this. Below 2/12, you must use a flat-roof or low-slope membrane system — shingles are simply not rated for those conditions.
Measuring from inside the attic is straightforward: bring a 24-inch level and a tape measure. Hold the level flat against the side of a rafter near mid-span. Adjust until the bubble is centered, then mark the point exactly 12 inches along the level from where it touches the rafter. Measure the vertical distance straight down from that mark to the top of the rafter. That measurement in inches is your rise, and your pitch is that number over 12. For example, if you measure 6 inches down, your roof is a 6/12 pitch. This technique is particularly valuable in winter or on very steep roofs where safely accessing the exterior is not practical.