Roof Truss Span Calculator
Span is the single most important number in roof truss design — the full wall-to-wall width the truss must cover. This roof truss span calculator takes your span and pitch and returns rafter length, run, rise, and roof height, in feet or meters.
Calculate Your Roof Truss Span
Enter your building specifications below. Results and the roof diagram update live as you type.
Live Roof Diagram
Results
Estimate Your Project Budget
Automatically calculated from your inputs above in the calculator.
Estimates only. Actual costs vary by region, supplier, and site conditions.
Understanding Roof Truss Span
Span is measured between the outside edges of the load-bearing walls, not the roofline. It is the number every other truss calculation builds from: run (half the span), rise (from pitch), rafter length (from rise and run), and ultimately roof area.
How far can you span a 2x6 truss? Roughly 20–24 ft, depending on grade, spacing, and load. How far can 2x4 trusses span? Engineered 2x4 trusses with web bracing can reach 30–40 ft in light residential loads, because the webs — not the chord alone — carry the span.
Enter your span in the calculator to see the resulting rafter length update instantly, then switch the unit toggle to metric if you're working in meters.
Frequently Asked Questions
What size truss for a 20 ft span?
A 20 ft (6.1 m) span typically uses 2x4 or 2x6 top and bottom chords depending on load, pitch and truss spacing (usually 24" on-center). Engineered trusses often use 2x4 members with web bracing for a 20 ft span, but always confirm with a stamped design for your snow/wind load.
How far can you span a 2x6 truss?
A 2x6 truss chord can commonly span roughly 20–24 ft depending on grade, spacing, pitch and load. Higher loads or wider spacing reduce the allowable span. Use the span calculator and verify against local building codes and an engineer's design.
How far can 2x4 trusses span?
Engineered 2x4 trusses can span up to about 30–40 ft in light-load residential roofs because the web members carry the load, not the chord alone. A single unsupported 2x4 rafter spans far less. Always confirm with an engineered, stamped truss design.