Rafter Length guide
Rafter Length: Material Planning Guide
A rafter length calculation produces a net geometric or quantity result, not a complete purchase order. Add ridge, tail, and field-trim allowances only after the geometric length is checked. Stock availability, cut sequence, fastening, finish build-up, waste, and whole-unit purchasing are recorded as separate decisions after the calculation is checked.
This topic now belongs to the complete guide
Rafter length is the geometric base for a later layout that includes ridge treatment, birdsmouth location, bearing, tail shape, fascia line, and site trimming. Keeping those additions outside the first triangle calculation makes it possible to identify whether an error came from geometry or joinery.
The purchasing pass starts from the unchanged net result, then records available stock lengths, sheet orientation, package quantities, offcut reuse, breakage, field trimming, and spare material as separate adjustments. This preserves the difference between what the geometry requires and what the supplier must deliver.
- Add ridge, tail, and field-trim allowances only after the geometric length is checked. Keep the net result unchanged for review.
- List stock size, package size, waste, and spare material on separate lines.
- Round purchase quantities only after the available product is confirmed.
For this tool, the calculation method is rafter length = √(run² + rise²) plus the sloped overhang. The consolidated page keeps this topic beside the worked method, material checks, source boundary, and printable record.
Last reviewed .