Roof Truss Calculator
Truss Parameters
Calculation Results
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How to Calculate Roof Trusses
- Number of trusses = building length ÷ spacing, plus 1. A 40 ft building at 24 in. on center needs 21 trusses; at 16 in., 31. Gable-end trusses are included in the count.
- Rise (truss height) = (span ÷ 2) × pitch. A 24 ft span at 6:12 rises 6 ft.
- Top chord (each side) = √((span ÷ 2)² + rise²), plus the overhang if you enter one. The overhang is measured level (horizontally) from the outside of the wall, so the calculator adds overhang ÷ cos(angle) along the slope: a 12-inch overhang adds about 13.4 inches of chord on a 6:12 roof.
- Bottom chord = the span.
The calculator sizes the layout, not the truss: truss lumber, plates and webs are engineered by the truss maker for your loads (snow, wind, dead load), and your building department will ask for the truss design drawings.
Roof Truss Examples
Example 1: 24 ft span, 6:12
24 in. spacing, 40 ft building
- 21 trusses
- Top chord: 13.42 ft each side (14.53 ft with a 12-inch horizontal overhang: 13.42 + 1 ft ÷ cos 26.57°)
- Truss height: 6 ft · Bottom chord: 24 ft
Example 2: 30 ft span, 4:12
24 in. spacing, 30 ft building
- 16 trusses
- Top chord: 15.81 ft each side · Truss height: 5 ft
Example 3: 28 ft span, 8:12
16 in. spacing, 40 ft building
- 31 trusses
- Top chord: 16.83 ft each side · Truss height: 9.33 ft
Example 4: Metric measurements
8 m span, 25°, 60 cm spacing, 12 m building
- 21 trusses
- Top chord: 14.48 ft (4.41 m) each side · Truss height: 6.12 ft (1.87 m)
How Much Do Roof Trusses Cost?
- A roof truss project costs about $16,500 on average, anywhere from $4,000 to $60,000 depending on the truss type and roof size; wood trusses run about $60-$500 each. Source: Angi, "How Much Do Roof Trusses Cost?" (2026 data).
- Metal trusses about $150-$700 each; labor $25-$75 per hour to set trusses, or $4-$10 per sq ft on new construction. Source: HomeAdvisor, "How Much Does a New Roof Truss Cost?", updated June 2026.
Truss prices depend on span, pitch, type (attic and scissor trusses cost more) and delivery; get a quote from a local truss maker with your span, pitch, spacing and loads.