Rough to Finished Calculator — Planing Allowances

A typical pass through a thicknesser removes 1.5–2mm from each face. To get flat, parallel faces from rough-sawn stock, expect to lose 2–3mm per face (4–6mm total thickness). Edge jointing typically removes 2–3mm per edge. Cupped or twisted boards lose more.

S1S = surfaced one side (one face planed flat). S2S = surfaced two sides (both faces planed parallel). S4S = surfaced four sides (both faces and both edges planed). Most furniture work requires S4S preparation.

Rough-sawn timber is cheaper per board foot but requires a jointer and thicknesser to prepare. Pre-planed (PAR — Planed All Round) is convenient but costs more and limits your thickness options. For furniture making, rough-sawn gives you more control over final dimensions.

PAR stands for Planed All Round, meaning all four long faces are machine-planed smooth. PAR timber from UK merchants is surfaced to standard finished sizes: e.g. 44×69mm from nominal 50×75mm rough, or 44×94mm from 50×100mm rough.