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Calculator · 2026

Roof truss calculator

How many roof trusses do I need?

Building length (inches) ÷ spacing, plus one. Trusses are typically spaced 24 inches on center, so a 40 ft building needs 21 trusses. A 24 ft span at 6/12 rises 6 ft from heel to peak.

What the numbers mean

  • Count: trusses along the building at the spacing, with one at each end (the gable-end trusses).
  • Heel to peak: half the span x pitch ÷ 12. Add the heel height (the truss depth at the wall) for the total height.
  • Top chord: half the span x the pitch factor, plus the overhang along the slope.
  • Bottom chord: the span.

Trusses are engineered. CMT Components, a truss maker, notes that the exact spacing and layout in your engineered truss drawings must be followed. Give the manufacturer the span, length, pitch, overhang and your local snow and wind loads; they size the members and plates. Rafters instead: rafter calculator.

Sources for the figures on this page

Truss spacing

Geometry for planning and quote checking, not structural design. Written by the Thomas Town Digital editorial team.

Roof truss questions

How many roof trusses do I need?

Divide the building length in inches by the spacing and add one for the end. At 24 inches on center, a 40 ft building needs 21 trusses (40 x 12 / 24 + 1), including the two gable ends.

How far apart are roof trusses?

Truss maker CMT Components: trusses are typically spaced 24 inches on center, but the spacing and layout in your engineered truss drawings govern.

How tall is a truss?

Heel to peak, half the span x pitch / 12. A 24 ft span at 6/12 rises 6 ft, plus the heel height at the wall.

Can I design my own trusses?

Trusses are engineered products, and the spacing and layout in the engineered truss drawings must be followed. Order them from a truss manufacturer, who sizes them for your span, loads and local code. Use this calculator to plan and to check a quote.