Rafters calculator
Rafter length and count for a gable roof from the span and pitch, plus the ridge board. A takeoff, not a span check.
Rafters
Done.
–Rafters
Need (exact)
Details
How we got it
rafter = (span/2 + overhang) × √(1 + (pitch/12)²); rafters = (⌈length ÷ spacing⌉ + 1) × 2
Estimate — check your local building code for structural parts.
Estimate only — bag yields vary by brand. Check your local building code.
How to use it
- Type your measurements. Feet-inch (12' 6 1/2"), decimal feet and metric all work; a bare number means feet or metres.
- Need is the exact amount. Buy rounds up to whole bags, sheets or pieces, with the waste % included.
- "How we got it" shows the formula, so you can check every number.
- A "Check this" note means a value looks unusual. Have a look before you buy.
Save it to a project
Keep this calculation with the job and add it to your shopping list. Free in your browser; price it and quote it with Pro.