Truss Calculator
A truss is the engineered triangular frame that supports a pitched roof. Sizing trusses correctly means getting the span, pitch, spacing, and member geometry right before ordering or building. This free truss calculator works through the whole simple truss calculator workflow: truss height, rafter length, total truss length with overhang, number of trusses, web member count, and an engineered truss cost estimate.
How the Truss Calculator Works
The basic truss geometry is a right triangle:
- Half span = building span / 2
- Truss height = half span * (pitch / 12)
- Rafter length = sqrt(half span^2 + height^2)
- Truss length with overhang = rafter length + overhang
This truss length calculator formula handles symmetric gable trusses with the peak at centerline. Asymmetric trusses and scissor trusses need different math (consult engineered drawings).
Roof Truss Design Calculator Basics
A roof truss design calculator picks truss type based on span:
| Span | Recommended Type | Webbing |
|---|---|---|
| Under 20 ft | King post | 1 vertical member |
| 20-30 ft | Queen post | 2 verticals + horizontal |
| Up to 40 ft | Fink (W-truss) | 4 diagonal/vertical members |
| 40-60 ft | Howe or parallel chord | Engineered only |
| Over 60 ft | Commercial engineered | Sealed drawing |
For most residential homes, the fink (W-truss) covers spans up to 40 ft with 2x4 chords and webbing.
Truss Length Calculator Example
For a 24 ft span, 6:12 pitch, and 12 in overhang:
- Half span = 12 ft
- Truss height = 12 * 6 / 12 = 6 ft
- Rafter length = sqrt(12^2 + 6^2) = sqrt(180) = 13.42 ft
- Truss length with overhang = 13.42 + 1 = 14.42 ft per top chord
This truss length calculator output is what you order from a truss plant per side.
Roof Truss Span Calculator
A roof truss span calculator validates whether your span is safe for standard 2x4 trusses:
- Span under 20 ft: 2x4 top chord at 24 in OC, 30 PSF live load
- Span 20-30 ft: 2x4 or 2x6 top chord at 24 in OC
- Span 30-40 ft: 2x6 required; engineer sealed drawing recommended
- Span over 40 ft: commercial engineered only
Double the spacing from 24 in to 16 in OC if adding snow load over 40 PSF, tile roofing, or solar panels.
Truss Cost Calculator / Roof Truss Cost
A truss cost calculator uses engineered truss pricing per linear foot of span:
- 2025 residential engineered truss (2x4 webbing): $3-6/ft of span
- Heavy engineered (2x6): $6-10/ft of span
- Pole-barn truss (gable, 20-40 ft): $6-12/ft of span
Roof truss cost example: a 40 ft x 24 ft ranch with 6:12 pitch and fink trusses at 24 in OC needs 21 trusses at ~$108 each = $2,268 for engineered trusses. Installation adds $2-4 per sq ft of roof area.
Roof truss prices home depot on 84 Lumber network: a pre-built 24 ft fink truss with 6:12 pitch runs $100-140 each, matching our estimate within 10%.
Truss Design Calculator vs Truss Analysis Calculator
A truss design calculator outputs geometry (height, length, member count) and cost. A truss analysis calculator solves the member forces under load (tension, compression in each member) using the method of joints or method of sections. This tool is a truss design calculator; use engineered software (MiTek SAPPHIRE, Alpine Software, or free tools like SkyCiv) for truss analysis.
Simple Truss Calculator Assumptions
A simple truss calculator makes standard assumptions:
- Symmetric gable truss: peak at centerline, equal slopes both sides
- Standard overhang: 12-24 in horizontal
- 2x4 chords at 24 in OC: covers spans up to 30 ft at standard residential load
- No point loads: uniform dead + live load
- Wood frame: SPF, SYP, or Doug fir; engineered trusses specify species
For scissor trusses, asymmetric designs, cantilevers, or commercial loads, always use an engineered truss design calculator with sealed drawings.
Truss Analysis Calculator Reference Numbers
Quick reference for truss member forces under uniform load (approximate):
- Top chord (rafter): compression, 2,000-5,000 lb at 40 PSF live load, 40 ft span
- Bottom chord: tension, equal magnitude to top chord
- Webs: alternating tension/compression, 500-1,500 lb each
Always cross-check with stamped engineering drawings before building.