How many trusses do I need for a 30 foot garage?

Carpentry & FramingIRC Wood Truss Sizing

Roof Truss Calculator

Calculate total engineered roof trusses required, top chord rafter cut lengths, and ridge height based on building dimensions and roof pitch.

Carpentry & Framing Field StandardsIRC Wood Truss Sizing

Engineering formulations calibrated to IPC, UPC & NEC specificationsSub-Zero Cold Climate Tolerances

Quick Summary & Key Answer

To calculate roof truss count, divide building length in feet by on-center spacing in feet, then add 1 for the end truss. For example, a 40-foot building with 24-inch (2-foot) truss spacing requires (40 / 2) + 1 = 21 total roof trusses (2 gable end trusses and 19 common interior trusses).

24" on-center is standard for residential trusses.
16" on-center is mandated in heavy snow load regions (>50 PSF ground snow).
Always install temporary diagonal bracing during truss crane hoisting.

Interactive Calculator

Adjust inputs for real-time results

Building Lengthfeet

feet

Building Span (Width)feet

feet

Roof Pitch

On-Center Truss Spacing

Eave Overhanginches

inches

Calculated OutputTruss Count Verified

Total Trusses Required

21trusses

Top Chord Rafter Length (with overhang): 16.65 ft
Ridge Peak Height above Top Plate: 7.00 ft
Gable End Trusses Required: 2 trusses
Common Interior Trusses: 19 trusses

Common Engineered Truss Profiles

The Fink (W-truss) is the most common residential configuration for spans up to 36 feet.

Frequently Asked Questions

Common questions regarding this calculation and code compliance

At standard 24-inch (2-foot) spacing, a 30-foot garage requires (30 / 2) + 1 = 16 trusses.