Translating units of measurement

Most technical texts contain units of measurement, and translating them correctly into the target language is critical. The field is vast, so here are three basics that often cause errors.

When not to convert units

Sometimes the right choice is not to convert. A classic case is bolt/screw sizes, whether specified in inches or millimetres. In the United States, standard sizes are 1 inch, 1 1/8 inch, etc. A Spanish-speaking engineer using U.S. fasteners will talk about 1 pulgada and 1 1/8 de pulgada, not 25.4 mm or 28.575 mm. Many manuals convert these inappropriately. Don’t make that mistake—when in doubt, ask the client or a seasoned colleague.

Another case: markings on the device itself. In “Fill the tank up to the 2-gallon mark,” you generally should not convert 2 gallons to 7.57 litres. The tank is probably marked in gallons, and the user must be able to find that mark.

Significant figures

When converting units, choose a sensible number of significant figures. Example from a TV manual:

Sit 10 feet from the screen.

A beginner might convert literally:

✗ Sit 3.048 metres from the screen.

That’s conceptually wrong: the writer means about 10 ft, not an exact distance. A correct translation would be:

✓ Sit 3 metres from the screen.

International System (SI)

Even the SI—used officially or de facto almost everywhere—doesn’t exempt us from adapting certain usages. Some prefixes are common in one language and rare in another: French technical texts often use daN (deca-newton), and German texts may use dag (decagram). In Spanish this is unusual, and many readers won’t recognise dag. The natural solution is to convert to newtons or grams (×10). The translator’s job is to make the text effortless for the reader—so smooth it doesn’t feel translated.