Common Timber Sizes — What You Actually Get
Common Timber Sizes — What You Actually Get
Rule of thumb for structural timber: 2mm off thickness, 5mm off width
CLS (Canadian Lumber Standard)
Already planed and rounded. Nominal = actual.
| 38 × 63 mm |
| 38 × 89 mm |
| 38 × 140 mm |
| 38 × 184 mm |
| 38 × 235 mm |
Structural Timber (C16 / C24)
| Sawn (nominal) | Finished (actual) |
|---|---|
| 47 × 50 | 45 × 45 |
| 47 × 75 | 45 × 70 |
| 47 × 100 | 45 × 95 |
| 47 × 125 | 45 × 120 |
| 47 × 150 | 45 × 145 |
| 47 × 175 | 45 × 170 |
| 47 × 200 | 45 × 195 |
| 47 × 225 | 45 × 220 |
Stock Lengths
2.4 — 3.0 — 3.6 — 4.2 — 4.8 — 5.4 — 6.0 m
Key Points
- • C16 = general structural use (most domestic work)
- • C24 = higher strength (longer spans, heavier loads)
- • Regularised timber is machine-planed on depth only (width stays rough)
- • Always check actual sizes when designing — a "47 × 100" joist is really 45 × 95
- • Treated timber (tanalised green) may swell slightly — allow for this in tight spaces
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