How we compute materials

Every number on CutlistHQ is derived from a documented public standard — none is guessed, and no value is originated by an AI model. Here is exactly what each calculation rests on.

Lumber dimensions

Actual dressed dimensions of softwood lumber (a 2×4 is 1.5″ × 3.5″, etc.) follow the US Department of Commerce Voluntary Product Standard PS 20. Board-feet are accounted by the standard rule, BF = (nominal thickness × nominal width × length-in-inches) ÷ 144.

Member sizing — from span tables, never estimated

Floor-joist and rafter sizes are taken from the American Wood Council / IRC residential span tables (16″ on-center, No. 2 SPF, conservative light accessory load). The engine looks each span up in the table. If a span exceeds the documented table, the tool refuses to assert a size and flags the structure as requiring an engineered design. We would rather show no number than a guessed one, because a wrong structural number is a safety hazard.

Member counts and roof geometry

Studs, joists, and rafters are counted by on-center spacing (count = ⌊run ÷ spacing⌋ + 1, inclusive of both ends). Rafter length comes from roof geometry: L = √(run² + rise²) + overhang, where rise = run × (pitch ÷ 12). Sheet-goods counts cover the floor, wall, and roof areas with a 10% cutting-waste allowance.

Cost

Costs are a national big-box midpoint estimate with a stated basis date on every page. They vary by region, cover framing materials only (not roofing, siding, doors, finishes, or hardware beyond framing), and should be treated as a planning estimate, not a quote.

What this is not

CutlistHQ is an estimating tool. It is not a permit-stamped engineered plan and does not assert code compliance. Always confirm local codes, load requirements, and permits with your building department.

Attribution: AWC Span Calculator · IRC R602/R802 · US DOC PS 20. Materials computed and published by the CutlistHQ editorial team.