Roof Pitch Calculator

A roof that drains well lasts longer and costs less over time. The Roof Pitch Calculator turns two simple measurements rise and run, into everything you need for layout and material choices. You get pitch in degrees, slope as percent, the classic x:12 ratio, and the rafter length for framing. Enter values in any single unit system.

What the Roof Pitch Calculator Does

The Roof Pitch Calculator turns two field measurements into the four numbers builders use every day: rafter length, pitch in degrees, percent slope, and the x:12 ratio. It standardizes units, converts between formats, and removes hand-calc errors that creep in when you’re tired or rushing a takeoff. You type rise and run once. The calculator does the rest.

Typical use cases

• Design & framing: Lay out a gable, shed, or dormer. Mark plumb and seat cuts with the degree output while you communicate the plan as x:12 on drawings.

• Roofing system selection: Check if your measured slope meets the minimum for three-tab shingles, metal panels, or single-ply membranes. Start with manufacturer manuals, then confirm against adopted codes in your jurisdiction.

• Accessory planning: Many skylight and solar kits publish angle ranges. Use the degree result to select the right flashing or racking without guesswork.

How to Use the Roof Pitch Calculator

You only need two measurements rise and run. Keep both in the same unit. Enter them once. The Roof Pitch Calculator returns the rafter length, pitch in degrees, percent slope, and the x:12 ratio you can read on the jobsite.

Inputs you enter (keep units consistent)

Outputs you get (what the tool calculates)

• Rafter length - the hypotenuse of the right triangle. Use it for cut lists.

• Roof pitch (deg) - the angle for saw bevels, PV tilt, and skylight kits.

• Roof pitch (%) - grade for drainage and civil tools.

• Roof pitch (x:12) - the carpenter’s ratio for quick field talk.

Formulas the Roof Pitch Calculator Uses

Get the math right and the build goes smoother. The Roof Pitch Calculator relies on right-triangle geometry to convert rise and run into rafter length, degrees, percent grade, and the x:12 ratio. Keep rise and run in the same unit.

rafter_length = sqrt(rise^2 + run^2)

pitch_degrees = atan(rise / run) * (180 / PI)

pitch_percent = (rise / run) * 100

pitch_x_per_12 = (rise / run) * 12