Pitch is the rise in inches for every 12 inches of horizontal run, e.g. 6/12.

What spacing should rafters use?

16 in on center is standard; 24 in is allowed with heavier lumber and lighter loads.

Rafter Calculator

Enter your roof run, pitch, and rafter spacing to calculate the rafter length and the number of rafters needed.

Estimates only. Round up and buy a little extra to account for waste, spills, and breakage.

Rafter length = run × √(1 + (rise/run)²). Rafters = roof length ÷ spacing + 1, doubled for both sides.

What is roof pitch?: Pitch is the rise in inches for every 12 inches of horizontal run, e.g. 6/12.
What spacing should rafters use?: 16 in on center is standard; 24 in is allowed with heavier lumber and lighter loads.

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