Writing Tip

Use the Proper Case for Units of Measurement and Metric Prefixes

Difficulty Level: Basic

Recommendation: Use the proper case for units of measurement and metric prefixes.

Although the major units of measurement of electricity are named after renowned scientists—Alessandro Volta, James Watt, André-Marie Ampère, Georg Simon Ohm, Heinrich Rudolf Hertz—when fully spelled out, they are cast in lower-case letters: volt, watt, ampere (amp), ohm, and hertz. When abbreviated, the abbreviations are capitalized: V, W, and A. The ohm is exceptional. Typically, a symbol is employed to abbreviate it (Ω). Hertz is also an exception, because its abbreviation merits two letters (Hz). Volt-ampere-reactive is also a special case, because there is no consensus on its capitalization. Var, VAR, and VAr are used with caprice. I recommend all caps.

For the most part, metric prefixes are lower case: deci (d), centi (c), milli (m), micro (µ, the Greek letter mu), and nano (n). The prefix for kilo is lower-case (k), but the abbreviated forms of the prefixes mega (M), giga (G), and tera (T) are capitalized. Examples: kV, mA, and GHz.

When in doubt, consult the following list of units of measurement relevant to electrical engineering (and other fields).

See Metric Units at Wikipedia