Roof Pitch Calculator: Angle, Ratio and Rafter

Roof Pitch Calculator

Find roof pitch, angle, slope percentage, rise and rafter line length from the measurements you know.

Length units

Calculate from

Horizontal run (ft)Level distance, not the sloped roof length.

Vertical rise (ft)

Pitch rise per 12Example: enter 6 for a 6:12 pitch.

Roof angle (degrees)

Slope (%)

Measured rafter line (ft)Must be at least as long as the horizontal run.

Overhang and display options

Horizontal eave overhang (ft)Adds the same slope beyond the entered run.

Rafter spacing (in, optional)Used only with roof length to estimate layout positions.

Roof length along ridge/eave (ft)

Roof pitch—

—Angle

—Slope

—Rise-to-run ratio

—Rise over entered run

—Rafter line over run

—Slope multiplier

—Rafter line including overhang

—Rafter layout positions

—Sloped area per plan area

Nearby common pitches

Pitch	Angle	Slope	Multiplier

Roof pitch formulas

Pitch rise per 12 = 12 × rise ÷ horizontal run. Angle = arctangent(rise ÷ run). Slope percentage = 100 × rise ÷ run. Slope multiplier = √(1 + (rise ÷ run)²). Rafter line length = horizontal run × slope multiplier.

Worked example

A roof that rises 6 ft over a 12 ft horizontal run has a 6:12 pitch, a 26.565° angle, a 50% slope and a 1.1180 multiplier. Its rafter line over that run is about 13.416 ft. With a 1 ft horizontal overhang, the sloped line to the eave is about 14.534 ft.

Pitch is not the same as roof area

This tool solves and converts the roof slope. For roofing squares, bundles and material allowance, use the general Roofing Calculator after measuring the roof plan. For full-length metal panels and trim, use the Metal Roofing Calculator.

Limits

Run is always horizontal. Do not enter an already sloped tape measurement as run.
The rafter result is a geometric line. It does not include ridge-board deduction, birdsmouth, heel height, fascia details, plumb cuts, seat cuts or lumber stock selection.
Rafter layout positions are a simple spacing count across the entered roof length, including both ends. Openings, hips, valleys, gables and doubled members are not included.
This calculator does not determine structural size, loading, connections, bracing, minimum drainage slope or code compliance.