Roof pitch, calculated instantly.

Roof pitch — sometimes called roof slope — is the steepness of a roof, expressed as the vertical rise over a 12-inch horizontal run. A “6/12 pitch” means the roof rises 6 inches for every 12 inches of horizontal distance. That number matters more than most homeowners realize: it decides which materials you can use, how walkable the roof is, how it sheds water and snow, and often adds 15-40% to installation cost as it gets steeper.

What is roof pitch, exactly?

Contractors express roof pitch three ways, and this calculator converts between all of them:

• Ratio (X/12). The most common US format. “6/12” = 6 inches of rise per 12 inches of run. Read aloud as “six twelve” or “six on twelve.”
• Degrees. The roof’s angle from horizontal. A 6/12 pitch is 26.57°. Used more often in engineering and by metal-roof installers.
• Percentage grade. Rise divided by run × 100. A 6/12 pitch is a 50% grade. Used in commercial roofing and on plans imported from Europe.

All three describe the same slope. Which one you use depends on who you’re talking to. If your contractor says “12/12” and your engineer says “45°,” they’re both correct.

How to measure roof pitch (3 methods)

1. From inside the attic (safest). Take a 24-inch level and a tape measure. Rest one end of the level against the underside of a rafter. Level it, then measure vertically from the 12-inch mark on the level down to the rafter. That measurement is your rise per 12 inches of run.
2. From the ground with a level and tape. Hold a level horizontally against the gable end so one end touches the roof edge. Measure the vertical gap from the far end of the level down to the roofline. Divide by the level’s length in inches, then multiply by 12 to get rise-per-12.
3. Using a phone level app. Most modern iPhones and Android phones include a level (Measure app on iPhone). Rest the phone flat on the roof surface — the angle it reports IS your pitch in degrees. Plug it into the calculator above to convert to X/12 or grade.

Common roof pitches by house style

US residential roofs cluster around a few standard pitches. The style of your house often predicts its pitch:

Pitch categories and what they mean

Flat and low-slope (0/12 – 3/12)

Anything below 4/12 is considered low-slope in most building codes. Asphalt shingles are generally NOT allowed below 2/12 by manufacturer warranty. You need a membrane system — TPO, EPDM, PVC, or built-up roofing. Ice-and-water shield is required on the entire surface, not just eaves and valleys.

Conventional (4/12 – 9/12)

Where most US homes live. Every mainstream roofing material is available. Walkable with normal precautions. Standard underlayment. Straightforward install. Cost premium: none.

Steep (10/12 – 14/12)

Above 9/12 crews charge a steep-pitch surcharge of typically 15-30%. They can’t walk it normally — they need roof jacks, harnesses, or scaffolding. Insurance premiums rise. Cleanup and staging take longer.

Very steep (15/12+)

Above 14/12 (roughly 50°) you’re looking at a 40-60% labor premium. Full harness required. Some materials (like heavy tile) become impractical because gravity works against installation. Shingles need six nails per shingle instead of four, and manufacturers may void warranty without specific fasteners.

Frequently asked questions

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