Millimeter vs. Millimetre — What's the Difference?

The term "millimeter" is the American English spelling for a unit of length in the metric system, equivalent to one-thousandth of a meter. It is widely used in the United States for measurements in science, industry, and everyday life. On the other hand, "millimetre" represents the British English spelling of the same unit, preferred in countries using British English, such as the UK, Australia, and Canada. Both terms are correct and refer to the same measurement of length.

In terms of usage, "millimeter" is typically seen in scientific and technical documents, manufacturing specifications, and any context where precise measurements are required in American English-speaking regions. Conversely, "millimetre" is used in similar contexts within British English-speaking countries, adhering to their spelling conventions for words ending in "-meter."

While there is no difference in the unit's application or size, the choice between "millimeter" and "millimetre" often depends on the regional or national conventions of the English language being used. This distinction is similar to other differences in American and British spelling, such as "color" vs. "colour" or "fiber" vs. "fibre."

Educational materials, textbooks, and scientific publications usually adhere to the spelling preferred by their target audience's language variant. For instance, American schools and journals use "millimeter," whereas British and Commonwealth countries opt for "millimetre."

Regardless of the spelling, the abbreviation for millimeter/millimetre remains "mm" in both American and British English, simplifying international communication and documentation where precise measurements are essential.