How to use this calculator
- Enter Building length in ft.
- Enter Spacing in in.
- Press Calculate. The highlighted row is your order quantity; the note beneath it translates the number into real-world terms.
Formula & constants
Trusses set at 24 in on-center: (building length in inches ÷ spacing) + 1. A 40 ft building needs 21 trusses at 24 in OC, 31 at 16 in OC. Every default in the fields above is editable — when your supplier’s spec sheet lists a different density, coverage rate or price, enter that number instead. The waste and compaction allowances follow common trade practice; see our methodology page for the derivation of each formula and the standards it references.
Where this fits in the project
Roof takeoffs start from the footprint corrected by pitch: get true area from the roof square footage calculator, convert to squares, then to shingle bundles or metal panels. Size gutters from the same perimeter measurement.
How this connects to your project
No quantity stands alone — each material in the chain depends on the ones around it. These are the planning steps that pair with the roof truss calculator:
- Roofing Calculator — Trusses form the roof structural framework.
- Roof Pitch Calculator — Pitch defines truss geometry and height.
- Roof Square Footage Calculator — Trusses support the roof surface area.
- Lumber Calculator — Trusses are constructed from dimensional lumber.
- Plywood Calculator — Roof sheathing attaches to trusses.
- Roofing Cost Calculator — Trusses are a significant roofing cost item.
Frequently asked questions
What spacing do roof trusses use?
24 in OC is standard for manufactured trusses; 16 in OC where heavy roofing (tile/slate) or point loads demand it.
Can trusses be modified on site?
Never cut or drill a truss without an engineer’s repair detail — every member is load-critical.
Last verified: — prices reflect current national averages. See our methodology.
Estimates are for planning. Material densities, coverage rates and prices vary by region and supplier — confirm final quantities before ordering, and check local code where structural or electrical work is involved.