Angle, percent slope and rafter multiplier for every common roof pitch, from 1/4 in 12 to 24 in 12. It fits on one sheet of letter paper, and it is free to print and hand out.
Angle, slope and rafter multiplier, 1/4 in 12 to 24 in 12
Pitch & Plank pitchandplank.com
How to read it. Pitch is the inches a roof rises for every 12 inches of level run. Find the pitch in the first column and read across. Multiply a level run by the multiplier to get the sloped length, or a flat area to get the roof area.
Example. A 6 in 12 roof with a 12 ft run to the ridge: 12 × 1.118 = 13.42 ft of rafter, or 13' 5", before the overhang.
Below 2 in 12: no asphalt shingles. Use a membrane, built-up roofing, roll roofing or standing seam metal.
2 in 12 up to 4 in 12: asphalt shingles need two layers of underlayment.
Over 4 in 12: OSHA counts it as a steep roof, so workers 6 ft or more up need guardrails, nets or a fall arrest harness.
8 in 12 and up: where an ice barrier is required, it must reach at least 36 in up the slope from the eave.
Rules from the 2021 International Residential Code, Section R905, and OSHA 1926.501, checked October 2026. Local codes and maker instructions can be stricter. Free to print and share. Calculators and a page for each pitch at pitchandplank.com
How the numbers are worked out
Each row comes from the same math as the roof pitch calculator, so the chart and the calculator always agree.
Angle = arctan(pitch ÷ 12)
Slope percent = pitch ÷ 12 × 100
Pitch multiplier = √(1 + (pitch ÷ 12)²)
Rafter per foot of run = 12 inches × pitch multiplier
Extra roof area = pitch multiplier − 1, as a percent
The rafter per foot of run is the same number found on the common rafter scale of a framing square. Lengths are rounded to the nearest sixteenth of an inch.
Each pitch in more detail
These pages have rafter lengths by building width, roof area and which roofing is allowed at each pitch.