Roof Rafter Framing Calculator

Rafter length, cut angles, and layout counts from a span and a roof pitch. Built for framers, roofers, and carpenters who need the number now, standing on the wall with a tape in the other hand.

Enter the building span and the roof pitch and read the answer in feet-inches-sixteenths, decimal inches, or metric. Every result shows all three, so it does not matter which one the crew works in.

COMMON RAFTER
In: building span, roof pitch as x/12 or degrees, ridge board thickness, and overhang. Out: rafter line length, total length with the tail, total rise, plumb cut angle, and level (seat) cut angle - the two angles that lay out a birdsmouth notch.

HIP AND VALLEY
Same span and pitch, plus hip or valley rafter length and its plumb cut angle, worked off the 16.97 run reference a framing square uses for a 45 degree corner.

RAFTER LAYOUT
In: wall or ridge length and an on-center spacing of 12", 16", 19.2", or 24". Out: number of spaces, rafters per side, total rafter count, and a board quantity to order against.

ROOF PITCH CONVERTER
Convert roof pitch between x/12, degrees, and percent slope. Type into any one of the three and the other two update as you go. Handy when the prints give you degrees and your framing square gives you twelfths.

SAVED CUT SHEETS
Name a calculation and keep it. Span, pitch, and results stay on the phone, so last week's roof is still there when the same detail comes up again.

ON THE JOB SITE
- Feet, inches, and sixteenths, the way a tape measure actually reads
- Decimal inches and metric (mm, cm, m) alongside every result
- Works with no signal and no data
- No account and no sign-up
- Free to use, with no trial period and no in-app purchases

Ads: a banner runs at the bottom of the screen, and saving a cut sheet may play a short video ad. If no ad is ready, the cut sheet still saves.

Rafter math is only as good as the measurements it is given. Check critical cuts, including birdsmouth depth, against your prints and local building code, and cut one and test-fit it before you cut thirty.