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Imperial to metric timber sizes (4x2 in mm and more)
Timber is still often called by its old imperial size, such as 4x2 or 6x2, but it is sold in millimetres. Enter an imperial size to see its nominal metric size and the nearest size we list. A 4x2 is 50 x 100mm nominal. Sawn sizes are nominal; planed (PAR) timber is smaller once it has been machined. You can also convert inches and fractions to mm, feet to metres and standard lengths such as 8ft to their metric trade length (2.4m).
Imperial timber size to metric (4x2 in mm)
What a 4x2, 3x2 or 6x2 is in mm, and the sections we list.
How it works
UK sawn convention: 1in ≈ 25mm nominal (4x2 = 100x50). Exact inch maths shown alongside.
Inches to millimetres
Inches (fractions like 1 1/2 allowed) to mm, or back.
How it works
mm = inches × 25.4. Example: 2in = 50.8mm.
Feet and inches to metres
Imperial lengths like 8ft or 6ft 6in in metres.
How it works
m = feet × 0.3048 + inches × 0.0254. Example: 8ft = 2.4384m.
Millimetres to inch fractions
The nearest 1/8, 1/16, 1/32 or 1/64 inch to a mm size, with the error.
How it works
Rounds mm ÷ 25.4 to the chosen fraction and shows how far off it is.
Standard lengths: feet to metres
The metric trade length a length in feet is sold as, in m and mm.
How it works
mm = feet × 304.8. Trade length = nearest 300mm step (8ft ≈ 2.4m).
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Square metres to linear metres
Linear metres of cladding, board-on-board or decking for an area.
How it works
lm = m² × 1000 ÷ cover (mm) × (1 + waste %). Decking cover = board width + gap. Board-on-board uses cover per pair.
Linear metres to square metres
How much area a run of boards will cover.
How it works
m² = lm × cover (mm) ÷ 1000. Example: 100lm at 132 cover = 13.2m².
Boards per metre of height
How many featheredge or cladding boards per metre up a wall.
How it works
Boards per metre = 1000 ÷ cover (mm), rounded up. 150 featheredge at 115 cover = 8.7, so 9.
Decking: boards, joists and screws
Total board metres, joist metres and screws for your deck, plus the per-m² rate.
How it works
Joists at 300mm for boards up to 22mm thick, else 400mm; 2 screws per board per joist (our decking calculator's defaults).
Cladding fixings per m²
Total fixings for your cladding area at your batten spacing.
Figures being checked. Fixing figures for featheredge and board-on-board are being checked.
How it works
Battens at up to 600mm centres (400 for diagonal). 2 fixings per board per batten for boards 100mm wide or more, else 1 (TDCA guidance). Featheredge and board-on-board are fixed differently, so no figure is given.
Sleepers: walls, beds and edging
Sleepers for a wall, raised bed or edging run, in our listed sizes.
How it works
Wall: m² ÷ (course height × length) × (1 + waste %), rounded up. Bed: perimeter × courses ÷ sleeper length, rounded up. Corner overlaps not deducted.
Sheet coverage
Sheets needed for an area, plus waste.
How it works
Sheets = area × (1 + waste %) ÷ sheet area, rounded up. Sizes are the sheets we list, or enter your own.
Timber volume (m³)
Cubic metres from thickness, width, length and quantity.
How it works
m³ = T(mm) × W(mm) × L(m) × qty ÷ 1,000,000. 10 × 47x100 at 4.8m = 0.2256m³.
Cubic feet and hoppus feet to m³
Swap between ft³, hoppus feet and cubic metres.
How it works
1ft³ = 0.0283168m³. 1 hoppus ft = 1ft³ × 4/π = 0.036054m³.
Board feet
Board feet from a timber size, with the m³ equivalent.
How it works
Board feet = T(in) × W(in) × L(ft) ÷ 12. 1 board foot = 144in³ = 0.00236m³.
Hoppus volume of a log
Quarter-girth (hoppus) volume for oak and round logs.
How it works
Hoppus ft = (girth ÷ 4)² × length (ft) ÷ 144. About 21.5% under true volume (π/4).
Timber weight (density) Figures being checked
Weight of beams or lengths by species, from published densities.
Figures being checked. Species densities and how they match our listings are being checked. Treat the result as a guide.
How it works
Weight = m³ × density (kg/m³). Densities: BS EN 338 class means and The Wood Database dried weights.
Van payload check
Will the load fit your van's payload? Uses your own payload figure.
How it works
Used = load + other weight, compared with the payload on your plate or handbook. No van figures are built in.
Angles and roof pitch
Degrees to ratio, % and rise per metre, plus rafter length.
How it works
Ratio = tan(angle). Rafter = run ÷ cos(angle) + overhang. Mono: run = span. Duo: run per side = span ÷ 2, ridge height = run × tan(angle). Not rafter sizing.
Questions
What is 4x2 in mm?
A 4x2 is nominally 50 x 100 mm. Once it's been regularised or planed it finishes smaller, and our treated 4x2 is 47 x 100 mm.
Why is 4x2 timber not exactly 4 by 2 inches?
The name is the nominal size before drying and machining. Planed timber loses a few millimetres from each face, so the finished size is smaller.
What is 8ft in metres?
8ft is 2.4384m. It is sold as a 2.4m trade length.
What is planed all round (PAR) timber?
PAR timber is planed on all four faces, which regularises it to a consistent size and finish but makes it about 6mm smaller than nominal (3mm per face).
About these converters
Each converter uses exact definitions (1 inch = 25.4mm, 1 foot = 0.3048m) and UK Timber's own listed sizes and cover widths. Results are a guide: check sizes and quantities against the product page before you order.