Roof Truss Calculator
Count the trusses and bracing needed for a building of any length.
What you'll need to order
- roof trusses
- hurricane ties
- lateral bracing lumber
- truss clips
Prices vary by region and haul distance. Get quotes from at least two local suppliers.
How this calculator works
trusses = (building length × 12 ÷ spacing) + 1
The "+1" accounts for the truss at both ends — a 40 ft building at 24 in spacing has 20 spaces but 21 trusses. Gable-end trusses differ from common trusses and are usually ordered separately.
Worked example
With building length 40 ft, truss spacing 24 in, truss span (building width) 30 ft, this calculator returns 21 .
Frequently asked questions
How many trusses do I need?
Divide the building length in inches by the spacing, then add one for the end truss. A 40 ft building at 24 inch centres needs 21 trusses.
What spacing should roof trusses be?
Twenty-four inches on centre is standard for residential work and lets you use 5/8 inch sheathing. Sixteen inch spacing is specified for heavy snow loads or where thinner sheathing is used.
Can I cut or modify a roof truss?
Never, without an engineer's approval. A truss is an engineered system in tension and compression — cutting any web or chord destroys its capacity, even if it looks like a redundant piece.
Do trusses need bracing?
Yes. Permanent lateral bracing along the bottom chord and web members is part of the design, not optional. Most truss collapses during construction happen because temporary bracing was inadequate.