Roof Truss Calculator
Estimate truss count and on-center spacing
Total length of the roof to be trussed
On-center spacing (e.g., 2 for 24")
Spacing
—
ft
Trusses Needed
—
trusses
Total Span
—
ft
Disclaimer: Results are estimates based on standard formulas. Not a substitute for professional advice from a licensed contractor, engineer, or architect. Verify all calculations before making purchasing or construction decisions.
How to Use This Calculator
Ordering roof trusses? Getting the count right avoids delays and material shortages. Our calculator figures truss count from your roof length and chosen on-center spacing.
- Measure the total length of the roof to be trussed
- Decide on truss spacing (24" on center is standard)
- Enter values in the calculator
- Order 1-2 extra trusses as spares for handling damage
Expert Insights
Smart analysis for your Roof Truss project
Spacing & Load Matching
24" OC suits most residential roofs, but high snow loads may require 16" OC. AI flags when climate zone loads call for tighter spacing.
Count & Waste Buffer
Always add one starting truss plus a spare. AI builds in a 5% handling buffer so you don't stall the crane waiting on a replacement.
Engineered vs. Site-Built
Pre-manufactured trusses are engineered, faster to install, and span further than stick-framed rafters. AI weighs span vs. cost trade-offs.
Calculation Formula
Trusses needed = ceil(Roof length / Truss spacing) + 1
The +1 accounts for the starting truss at the beginning of the run.
Total span = Roof length
Roof Truss Type Comparison
| Truss Type | Typical Span | Best Use | Spacing | Relative Cost |
|---|---|---|---|---|
| Fink (W) | 20-40 ft | Standard residential | 24" OC | Low |
| Attic / Room-in-Attic | 30-50 ft | Living space in attic | 24" OC | High |
| Scissor | 20-40 ft | Vaulted ceilings | 24" OC | Medium |
| Hip | 30-60 ft | Hip roof construction | 24" OC | Medium-High |
| Stick-Framed Rafters | Variable | Custom / small spans | 16" OC | High (labor) |
Authority References
Our calculations are based on guidelines and standards from these authoritative sources:
- Structural Building Components Association (SBCA) — Truss Design & Installation Standards. Learn more
- Truss Plate Institute (TPI) — ANSI/TPI 1 National Design Standard for Metal Plate Connected Wood Trusses. Learn more
- International Residential Code (IRC) — Section R802 — Wood Roof Framing. Learn more
Frequently Asked Questions
How far apart should roof trusses be spaced?
Standard truss spacing is 24 inches on center for residential roofs. Trusses can be spaced 16 inches on center for heavier loads or 48 inches for engineered trusses designed for wider spacing.
How do you calculate the number of trusses needed?
Divide the roof length by the truss spacing, then add one for the starting truss. For example, a 40 ft roof with 2 ft spacing needs 21 trusses (40 / 2 + 1).
How much do roof trusses cost?
Pre-manufactured roof trusses cost $60-$500 each depending on span and complexity. A typical 2,000 sq ft home uses 25-40 trusses, totaling $1,500-$15,000.