I write about radios a lot, and use the abbreviation MHz and kHz with frequencies, but I’ve always wondered why one is capitalized and the other is not. I asked ChatGPT:
Why is the first letter of the abbreviation MHz usually capitalized, but the first letter of kHz is not?
ChatGPT replied:
The reason for this difference in capitalization between “MHz” and “kHz” has to do with the SI (International System of Units) rules for unit symbols.
In the SI system, unit symbols are always written in lowercase letters, except when the symbol is derived from a proper noun. In the case of “MHz”, the unit is derived from “megahertz”, which is a combination of the metric prefix “mega-” and the unit “hertz”. Since “mega-” is a proper prefix derived from a Greek word meaning “great”, the first letter of the symbol “MHz” is capitalized to indicate this derivation from a proper noun.
On the other hand, “kHz” is derived from “kilohertz”, which is also a combination of the metric prefix “kilo-” and the unit “hertz”. However, “kilo-” is not a proper prefix in the same way that “mega-” is, so the symbol “kHz” does not capitalize the first letter.
It’s worth noting that while these rules are widely followed, there may be variations or exceptions depending on the specific context or style guide being used.
I didn’t quite follow the rationale, so I asked a follow-up question:
Continue readingSo why is “kilo-” not a proper prefix, but “mega-‘” is?