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The measurement in centimetres.
Usually a figure read off a tape or a ruler. If it came from a construction drawing it is almost certainly already in millimetres — metric drawings are dimensioned in millimetres with the unit left off entirely.
Length
125 mm
The prefixes define it: a centimetre is one hundredth of a metre and a millimetre one thousandth, so 1 cm = 10 mm. Exact by definition; the risk here is the decimal point, not the factor.
- Same length in metres
- 0.13 m
- Same length in inches
- 4.92 in
They open the calculator with your figures already in it
Centimetres to Millimetres Calculator: 125 mm — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
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How this was calculated
Formula source(s)
- SI prefixes (BIPM SI Brochure): centi- = 10⁻², milli- = 10⁻³, so 1 cm = 10 mm by definition
Inputs used
- Length (cm)
- 12.5
Intermediate steps
- Same length in metres
- 0.13 m
- Same length in inches
- 4.92 in
Confidence note: The prefixes define it: a centimetre is one hundredth of a metre and a millimetre one thousandth, so 1 cm = 10 mm. Exact by definition; the risk here is the decimal point, not the factor.
Add the equipment this sizes
This result is a specification — 125 mm — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.
Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.
Sources checked 2026-09-11 · v1.0.0
Regulatory standards & verification citations1
- SI prefixes (BIPM SI Brochure): centi- = 10⁻², milli- = 10⁻³, so 1 cm = 10 mm by definition
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The two metric units that sit either side of the line between talking about a dimension and building to it. People speak in centimetres — a hand's width, a rough gap, a sketch on the back of a delivery note — and then the same figure has to enter a cut list, a drawing or a CNC file, where the unit is millimetres and always has been. The conversion itself is trivially a shift of the decimal point, which is exactly why it is worth doing deliberately: an error of one place here is an order of magnitude, it produces a number that still looks plausible, and it survives all the way to the saw.