Writing units of measurement

In almost the entire world, the International System of Units (SI) is the legal system of measurement. Any technical translator must know it to do the job properly.

The SI defines the units for different physical quantities and how to express those units. The official list of units is set by the International Bureau of Weights and Measures (BIPM) and is available in English and French. In this article we focus on how to express those units—and, more specifically, on unit symbols. 

Magnitudes fundamentales

Main derived quantities

Notes on writing

• Unit symbols are not abbreviations and therefore take no full stop.

  • Correct: Make a mark 0.2 m from the end.

  • Incorrect: Make a mark 0.2 m. from the end.

• Symbols do not take plural s: 5 kg (not 5 kgs).

• For products and quotients use the middle dot (·) and the slash (/), or negative exponents.

  • Correct: The price of kW·h is €0.15 in the retail market.

  • Admissible: The price of kWh is €0.15 in the retail market.

  • Incorrect: kW x h.

• The second has the symbol s.

  • Correct: Wait at least 8 s before opening the door.

  • Incorrect: Wait at least 8 sec. before opening the door.

• Some non-SI units have official symbols: minute (min), hour (h), degree (°), tonne (t).

Additional information
The official website of the BIPM (International Bureau of Weights and Measures) offers extensive information in English and French.

© 2025 Alejandro Moreno Ramos, www.ingenierotraductor.com