3 x 4 inch treated timber
“3 × 4” is the traditional imperial designation for timber formerly supplied at 3 inches by 4 inches. Since the UK’s move to metric, timber is specified in millimetres.
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Nominal imperial size: 3" × 4" (≈ 76.2 × 101.6 mm)
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Nominal metric reference: 75 × 100 mm (orientation may be shown as 100 × 75 mm)
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Typical finished/regularised size after drying and planing:
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Planed (PSE/PAR): ≈ 70–74 mm × 94–97 mm
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Sawn/regularised carcassing: ≈ 72–75 mm × 97–100 mm
(Actual dimensions vary by mill, grading, moisture content, and finish.)
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The legacy “3×4” label remains in trade use, but orders, drawings, and cutting lists should be based on the metric finished size. For tight tolerances or when matching existing work, measure the actual section supplied. If used structurally, confirm the grade (e.g., C16/C24). Lengths are supplied in metres.
