Truss Calculator (Metric)
Enter your building length and truss spacing to get the number of roof trusses you need.
What your result means
Trusses is the total count for the run, including the one at the end since a length never divides evenly. Trusses are engineered units, so never cut or modify one on site, and order the gable-end trusses separately because they're framed differently. Follow the manufacturer's bracing spec during install.
How to use this calculator
- Measure building length (the direction trusses span across).
- Standard truss spacing is 61 cm OC.
- Use 40.6 cm OC for heavy snow loads or tile roofs.
- Read truss count.
- Trusses are engineered - have manufacturer review design.
The formula
Convert the building length to inches, divide by the spacing, round up for the bays, and add one for the end truss.
Worked example
Say your building is 12.2 m long with trusses 61 cm on center. That's 1219.2 cm divided by 24, which is 20, plus one end truss, so 21 trusses.
Truss spacing by load
| Spacing | When to use |
|---|---|
| 61 cm OC | Standard residential |
| 40.6 cm OC | Heavy snow loads or tile roofs |
Tips & gotchas
- 61 cm on-center is the residential standard.
- Drop to 40.6 cm on-center for heavy snow loads or a tile roof.
- Trusses are engineered. Never modify one on site.
- Order gable-end trusses separately; they're framed differently.
- Bracing during install is critical, so follow the truss manufacturer's spec.
Frequently asked questions
How far apart should roof trusses be?
61 cm on center is standard, 16 for heavy loads.
Can I make my own trusses?
No. Trusses are engineered. Buy them from a truss manufacturer.
How long does it take to install trusses?
A crew with a crane can set 30-plus a day.
Can I cut a truss to fit?
Never. They're precisely engineered, and cutting one voids the design.
Are trusses cheaper than rafters?
Yes for production homes, since they go up fast. Rafters are more flexible for custom builds.
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