Construction Calculators

Roof Truss Calculator

Calculate the number of roof trusses needed to frame a roof of a given length at a chosen on-center spacing.

Trusses needed —

About the Roof Truss Calculator

This calculator estimates how many prefabricated roof trusses you need to frame a roof of a given length. Trusses are set at equal intervals along the building, so the count is one more than the number of spacing gaps.

Formula: Trusses Needed = (Roof Length ÷ Spacing in Feet) + 1

24in o.c. is the most common truss spacing for residential roofs, while 16in o.c. is used for heavier roof loads like snow country or tile roofing. Gable-end trusses and any girder trusses at openings may need to be ordered as special configurations.