Wood Roof Truss Calculator — ft, lumber
How to use this calculator
Select a truss type, enter the span, roof pitch (rise per 12″ run), spacing, and building length. Choose chord and web member sizes. The calculator computes truss height, rafter length, number of trusses, and total board feet of lumber needed.
Truss types — King Post (simple, short spans), Queen Post (medium spans), Fink/W (most common residential), Howe (heavier loads).
Lumber — board feet = width(in) × depth(in) × length(ft) / 12.
Saved Calculations
| Time | Type | Span | Pitch | Trusses | Total BF | Cost |
|---|
How to Calculate Wood Roof Truss Lumber
This calculator estimates lumber quantities for common residential roof truss types. Enter the building span, roof pitch, truss spacing, and building length. The calculator determines the number of trusses, rafter length, truss height, web member count, and total board feet of lumber.
Formulas
Rise = (span/2) × (pitch/12). Rafter length = √((span/2)² + rise²) + overhang/cos(angle). Number of trusses = building length / spacing + 1, rounded up. Board feet = nominal width(in) × nominal depth(in) × length(ft) / 12.
Truss Types
King Post — simplest, one vertical web at center, best for spans up to 20 ft. Queen Post — two vertical webs with horizontal tie, spans 20–30 ft. Fink/W — most common residential, V-shaped webs, efficient for 24–32 ft spans. Howe — vertical webs in compression, diagonal webs in tension, good for heavier loads.
FAQ
What spacing should I use? 24″ on center is standard for residential construction. Use 16″ for heavier loads or longer spans.
