Length Unit Converter
Metres, millimetres, feet and inches — every unit shown at once.
Inputs
Result
Formula
| Metric | 1 m = 10 dm = 100 cm = 1000 mm, 1 km = 1000 m |
| Imperial | 1 ft = 12 in, 1 yd = 3 ft, 1 mile = 1760 yd |
| Metric to imperial | 1 in = 25.4 mm, 1 ft = 0.3048 m |
| Chinese units | 1 chi = 1/3 m ≈ 333.33 mm, 1 cun = 33.33 mm |
| General rule | target = source value × source factor ÷ target factor |
1 metre converts to 3.2808 ft, 39.3701 in or 1000 mm. A 3.5 m floor height is 11.4829 ft, and a 1220 × 2440 mm sheet is exactly 4 ft × 8 ft.
Length unit conversion factors
| Unit | Symbol | In metres | In millimetres | Typical use |
|---|---|---|---|---|
| Metre | m | 1 | 1000 | Drawings |
| Millimetre | mm | 0.001 | 1 | Bar size, slab depth |
| Centimetre | cm | 0.01 | 10 | Fit-out dimensions |
| Kilometre | km | 1000 | 1000000 | Road distance |
| Inch | in | 0.0254 | 25.4 | Pipe size, imperial drawings |
| Foot | ft | 0.3048 | 304.8 | 4×8 sheets |
| Yard | yd | 0.9144 | 914.4 | Earthwork, fabric |
| Mile | mi | 1609.344 | 1609344 | Highway distance |
| Chinese chi | chi | 0.3333 | 333.3 | Spoken fit-out quotes |
FAQ
Why can't inches and feet be handled as decimals?
Imperial is duodecimal: 1 ft = 12 in, 1 yd = 3 ft, 1 mile = 1760 yd. The commonest mistake on imperial drawings is padding with zeros — writing 3 ft 6 in as 3.6 ft when it is 3.5 ft, a 30 mm error. Convert everything to inches first, then divide by 12.
What does a “4 fen” pipe mean in millimetres?
Here “fen” is 1/8 inch, so a 4 fen pipe is 1/2 inch = 12.7 mm, i.e. DN15 with roughly 21.3 mm outside diameter. Note that DN is neither bore nor OD — galvanised steel follows the bore series and plastic follows the OD series, so match fittings on outside diameter, not on the “fen” label.
How different are the Chinese chi and the foot?
One chi is 333.33 mm against 304.8 mm for a foot, so the chi is 9.4% longer. Quotes “by the chi” are common in fit-out work with nobody stating which chi, and a 9% error across tens of metres adds up — confirm and write it on the order.
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Results are estimating aids only and are not a design basis. Construction and final accounts must follow the drawings, the applicable standards and an approved method statement. Anything affecting structural safety, shoring or falsework must be checked by a suitably qualified engineer.