millimetre (mm)
1 millimetre = 0.001 metres
What is millimetre?
A millimetre is a metric unit of length equal to one thousandth of a metre. It is used in precision manufacturing, medical imaging, engineering tolerances, and detailed technical specifications.
Notes: Metric unit
Real-world uses
Millimetres are essential in precision engineering, machining tolerances, and manufacturing specifications. Rainfall is reported in mm by meteorological services worldwide. Dentists measure cavity depths and orthodontic adjustments in millimetres.
History
Part of the original French metric system from the 1790s. The prefix "milli-" derives from the Latin "mille" meaning thousand, indicating one-thousandth of a metre. It became critical with the rise of precision manufacturing in the Industrial Revolution.
Common mistakes
Confusing millimetres with centimetres when reading rulers—each small division on a metric ruler is 1 mm, not 1 cm. Also, mixing up mm with mils (thousandths of an inch) in engineering contexts.
When is this conversion used?
This conversion is frequently needed in construction, architecture, and real estate where building codes may specify dimensions in one system while materials are sold in another.
How to convert millimetre to metre
To convert millimetre to metre, multiply the value by 0.001.
Conversion formula (from base unit)
x * 0.001
Measurement standards
The metre is one of seven SI base units, maintained by the International Bureau of Weights and Measures (BIPM). Since 2019, it is defined by fixing the numerical value of the speed of light in vacuum to exactly 299,792,458 metres per second.
Did you know?
A human hair is roughly 70 micrometres wide, while a single gold atom measures about 0.144 nanometres in diameter — meaning you could line up nearly half a million atoms across the width of one hair.
| millimetres | metres |
|---|---|
| 0.1 | 0.0001 |
| 0.5 | 0.0005 |
| 1 | 0.001 |
| 2 | 0.002 |
| 5 | 0.005 |
| 10 | 0.01 |
| 25 | 0.025 |
| 50 | 0.05 |
| 100 | 0.1 |
| 250 | 0.25 |
| 500 | 0.5 |
| 1,000 | 1 |
Common values
| millimetres | metres | |
|---|---|---|
| Height of a door | 2,100 millimetres | 2.1 metres |
| Basketball court length | 28,000 millimetres | 28 metres |
| Football field (soccer) | 105,000 millimetres | 105 metres |
| Marathon distance | 42,195,000 millimetres | 42,195 metres |
| Altitude of a cruising airplane | 10,668,000 millimetres | 10,668 metres |
Full millimetre conversion table
| Unit | Value | Factor |
|---|---|---|
| metre | 1 mm = 0.001 m | × 0.001 |
| kilometre | 1 mm = 0.000001 km | × 0.000001 |
| centimetre | 1 mm = 0.1 cm | × 0.1 |
| inch | 1 mm = 0.03937008 in | × 0.03937008 |
| foot | 1 mm = 0.00328084 ft | × 0.00328084 |
| mile | 1 mm = 6.213712e-07 mi | × 6.213712e-07 |
| yard | 1 mm = 0.00109361 yd | × 0.00109361 |
| micrometre | 1 mm = 1,000 µm | × 1,000 |
| nanometre | 1 mm = 1,000,000 nm | × 1,000,000 |