Roof Pitch Calculator

Pitch, explained the way roofers use it

Roofers do not talk in degrees; we talk in rise over run. A "six twelve" rises 6 inches for every 12 inches of horizontal travel. The notation survives because it is how you actually build and measure: set a level, measure 12 out, measure the drop. Degrees are what you need when a spec sheet, a solar installer, or a drone app speaks math instead of carpentry, so this tool converts both directions.

The conversion is straight trigonometry: the angle is the arctangent of rise divided by run. A 4/12 is 18.4 degrees, 6/12 is 26.6, 9/12 is 36.9, and 12/12 is a perfect 45. Past 12/12 you are into mansards and A-frames, where the "run" is shorter than the rise and most standard tables stop.

Why pitch matters more than most people think

• It gates your material choices. Shingles are code-legal down to 2/12 (with beefed-up underlayment from 2/12 to 4/12). Below that, water moves too slowly and wind pushes it uphill: membrane or standing seam territory.
• It multiplies your surface area. The same footprint carries 5 percent more roof at 4/12 and 25 percent more at 9/12. That flows straight into materials and cost.
• It multiplies labor. Somewhere around 7/12, production slows and safety equipment becomes mandatory. Around 10/12, add staging. Bids reflect this honestly; our cost estimator charges +10 percent for steep and +20 percent for very steep for exactly this reason.
• It changes how long the roof lasts. Steeper roofs shed water and debris faster, dry quicker, and generally outlive their gentle-sloped twins by a meaningful margin.

Common pitch situations

Mixed-pitch homes. Lots of houses run a 6/12 or 8/12 main roof with a 3/12 porch or addition. Treat them as separate roofs: they may need different materials at the transitions, and low areas often need ice and water membrane even where the main field does not.

"It looks flat but it is not." A 1/12 or 2/12 roof reads as flat from the ground. People shingle these because they look shallow enough, and then the ceiling stains show up in February. Measure before assuming: this calculator plus a level settles it in two minutes.

Estimating from a photo. You can eyeball pitch from a gable end: compare the roof triangle's height to half its width. If the peak rises half of the half-span, that is a 6/12. It is a rough method, fine for budgeting, not fine for ordering steep-charge labor.