Roof Truss Calculator
Count roof trusses by building length and spacing.
Enter the building length and your truss spacing to get the number of roof trusses required. The estimate adds one truss because both end walls need one.
How it works
Divide the building length (in inches) by the on-center spacing to get the number of spaces, then add one for the final truss. Trusses are commonly set 24 inches on-center; 16-inch spacing is used for heavier loads.
Frequently asked questions
How many roof trusses do I need?
Divide building length in inches by the spacing and add one. A 40-ft building at 24-inch spacing needs about 21 trusses.
What is standard truss spacing?
24 inches on-center is most common for residential roofs; 16-inch spacing is used for heavier loads or certain sheathing.
Does this count gable-end trusses?
The +1 covers the end truss. Gable-end trusses are a different (vertical-web) type — confirm your design with the truss supplier.
Is this calculator free and private?
Yes. Every CubicCabin calculator runs entirely in your browser, so the numbers you enter are never uploaded or stored. There's no sign-up, no limits, and it keeps working even if you lose connection after the page loads.