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Timber conversion calculator
Our free timber conversion calculator puts the sums you need for a timber project in one place. Convert inches to millimetres and feet to metres, find out what 4x2 is in mm, and turn square metres into linear metres for cladding and decking using real cover widths from our range. You can also work out boards per metre of height, decking boards, joists and screws, sleepers for walls and raised beds, sheet coverage, volume in m³, cubic and hoppus feet, board feet and roof pitch. Pick a tool from the list or search for it, enter your figures and the answer appears straight away. Results are a guide: check measurements on site and allow for waste.
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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.
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).
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.
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.
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.
How do I convert m² to linear metres?
Divide the area in m² by the cover width in metres. For example, 10m² of shiplap with a 132mm cover needs 10 ÷ 0.132 = 75.8 linear metres, before waste.
How many featheredge boards do I need per metre?
Divide 1,000 by the cover width in mm and round up. A 150mm featheredge board at 115mm cover gives 8.7, so 9 boards per metre of height.
How do I work out m³ of timber?
Multiply thickness (mm) × width (mm) × length (m) × quantity, then divide by 1,000,000.
What is a board foot?
A board foot is 144 cubic inches: 1 inch thick, 12 inches wide and 1 foot long. 1m³ is about 423.8 board feet.
What is a hoppus foot?
An old measure for round and square timber volume, still used for oak and logs. One hoppus foot is about 1.27 cubic feet (0.036m³).
How much waste should I allow?
We default to 10% for cladding and decking; increase it for complex shapes, many cuts or short lengths.
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.