How do you calculate roof pitch from a tape measure?

Roofing
Layout
Estimating & Takeoff

Rafter length, plumb cuts and birdsmouths all fall out of pitch, and getting it wrong is discovered when a rafter will not seat on the top plate. Saving the span on the T1 Tomahawk and passing it to the roof pitch utility halves the run and deducts the ridge without pencil arithmetic on a shingle wrapper, and rise, rafter length, angle and slope come back together. One trip up, and the cut list is already right.

How pitch turns into a cut list

Span saved on the T1, not on a shingle wrapper
Ridge deducted and run halved automatically
Rafter length, pitch angle and slope returned
Plumb cut and birdsmouth work off one figure
One trip up the ladder for the whole set

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Measure the full span, subtract the ridge thickness, then divide by two to get the run for one side. Save that reading, open the roof pitch utility, and enter the run and the rise. Rafter length, pitch angle and slope calculate themselves. No pencil math on a shingle bundle, and no second trip up the ladder to check it.