Electronic – the correct spelling/capitalization of watt hour


In some documentation I have commented that a field contains "the forward active power, in Wh". Which way should it be written (when I don't want to use the abbreviation)?

  1. the forward active power, in watt hours
  2. the forward active power, in Watt hours
  3. the forward active power, in watt-hours
  4. the forward active power, in Watt-hours

On the wikipedia page for kWh they seem to use both hyphenated and non-hyphenated versions. I don't see "watt" being capitalized there. Is there a standard? This may be more of a question for english.stackexchange.com, not sure.

Best Answer

According to the IEEE/ANSI standard, the acceptable spellings for Wh, when it is written out, are

watt hour (preferred)

The names of SI units are not capitalized unless they are used in a situation where any word would be capitalized, such as the beginning of a sentence. Of course, the standard unit of energy would be the joule so the watthour is more of a colloquialism anyway.

EDIT: The standard that defines usage of SI units is IEEE/ASTM SI 10-2010, "American National Standard for Metric Practice".