Roof Truss Calculator
Trusses repeat along the building's length at a fixed on-center spacing (commonly 16, 19.2 or 24 in). This calculator gives the truss count, the gable-end count if you need them, and the actual spacing once trusses are evenly divided over the run.
The worksheet
roof truss calculator18 trusses total (16 common + 2 gable-end), at 24 in actual spacing.
| Building length | 30 ft (360 in) | |
| Target spacing | 24 in o.c. | |
| Common trusses = ceil(length / spacing) + 1 | 16 | |
| Gable-end trusses | 2 | |
| Total trusses | 18 | |
| Actual spacing once evenly divided | 24 in |
Framing hardware for rafters, trusses & joists
18 trusses total (16 common + 2 gable-end), at 24 in actual spacing. Connectors, hangers and fasteners sized to the framing you just calculated. A lumber yard or supplier can also cut and engineer trusses to spec.
Simpson Strong-Tie–style joist hangers, rafter ties and hurricane clips for code-compliant framing connections.
Shop framing connectorsMetal truss plates, ridge straps and rafter brackets for built-up or repaired roof framing.
Shop truss hardwareSome links are affiliate links: if you buy through them we may earn a commission at no extra cost to you. These are starting points, not engineering endorsements. Always confirm a product's rated snow load meets the design load above.
Notes
- Truss spacing must match your roof sheathing's span rating (check the panel's APA stamp) and your local snow/wind load requirements; lighter loads can sometimes use wider 24 in spacing, heavier loads often need 16 in.
- This counts trusses only. Always follow the truss manufacturer's stamped placement and bracing drawings: every roof truss is an individually engineered structural component, not interchangeable with a generic rafter.
- Add extra trusses (or girder trusses) at large openings, valleys, hips, or anywhere mechanical equipment bears on the roof.
Notes & questions
01How many trusses do I need for a 40 ft roof?+
At 24 in o.c. spacing with gable ends, a 40 ft building needs 21 common trusses plus 2 gable-end trusses (23 total); enter 40 above with your spacing to confirm.
02What truss spacing should I use?+
16 in o.c. is common for heavier roof loads (shingles, snow-load regions); 24 in o.c. is common for lighter, metal-roofed buildings. Your roof's design loads and sheathing span rating set the requirement, so confirm with your truss supplier or engineer.