New Zealand · metal roofing
Rafter length calculator
Common rafter = run / cos(pitch). Hip = √(run² + run² + rise²) on an equal-pitch rectangular hip.
Run is half the eave-to-eave span plus the eave overhang (gable/hip) or the full plan width plus overhang (skillion). Rise is run × tan(pitch). The metal sheet is cut to the same slope as the common rafter, plus whatever you need for a drip and a ridge tuck — this tool treats sheet length as that slope length and then rounds up 50 mm.
Hip length here is the 3D hip rafter, which is also a decent first length for a hip flashing. Valley length, when you type a valley count, uses the same figure on a hip and the common-rafter length on a gable (typical lean-to intersection).
Birdsmouth, plumb cut and ridge thickness are carpentry. MyCarpentry-style framing detail is not duplicated here on purpose — this site is a cladding takeoff.
FAQ
Does sheet length equal rafter length?
Almost, on a simple ridge-to-eave lay. You may add for an eaves overhang already in the run, a ridge tuck, or a birdsmouth that shortens timber but not the sheet. Check the detail.
What about unequal pitch hips?
Not in v1. Split the roof into sections and treat the valley/hip as a measured length instead.