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Should the unit "Ohm" be capitalized or not? For example, "kOhm" versus "kohm" vs "kΩ", which is most correct?

Alex I
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    I would say it is matter of preference. IMO: kΩ > kOhm > kohm – Marco Dec 31 '15 at 07:51
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    SI standard says use lower case for units named after somebody when written out long form and capitalise the first letter for the symbol. V for volt, A for ampere, Hz for hertz, Ω for ohm, etc. – Transistor Dec 31 '15 at 10:22
  • @transistor right, but kohm looks like a hybrid: long "ohm", but contracted "kilo". – Ruslan Dec 31 '15 at 12:51

2 Answers2

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In my experience "kΩ" is preferred, but if you don't have the "Ω" symbol available on your computer then you need to write out the full words in lowercase: "kilo ohm".

See here for the standards on writing out SI units: International System of Units

The Wikipedia article on the ohm says it should be "kilohm" (not "kiloohm") if written out, which I've not seen in my experience, but I'll include this for full reference.

Velvel
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archaeopteryx
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    Just going to add this here to justify the need to write out the word if the symbol is lacking http://www.poynton.com/notes/units/ "Write a numeric value with units in either the journalistic style, using prefix and unit names (four kilohertz); or the scientific style, using prefix and unit symbols (4 kHz). Don't mix these styles: Do not mix a prefix name with a unit symbol (WRONG: kiloHz), or a prefix symbol with a unit name (WRONG: kHertz). Avoid "abbreviations" for units (WRONG: sec., amp); use the unit names or symbols instead. " – Dave Dec 31 '15 at 08:30
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    @Chu, That's the Symbol. ampere = A, volts = V, ohms = Ω (this is a capital Omega), coulomb = C, hertz = Hz, etc. NOT THE NAME, which is always written lowercase. All of these have capitals for their SYMBOLS unlike say meter = m, second = s, gram = g, etc. – Dave Dec 31 '15 at 08:50
  • @Dave, yes that's correct, I'll delete my original comment. – Chu Dec 31 '15 at 09:03
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    "kilo ohm" is wrong. SI prefixes are not spaced from the units. e.g. "millimeter", not "milli meter". – Transistor May 21 '22 at 12:30
  • Tip: You can type Ω by holding Alt key and type '234' (release Alt now). Alt + 230 = µ for µF. I'm on Windows, dunno about Macs. – troubleshooter Jul 16 '23 at 05:48
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As per the standard convention whenever the SI unit is written it is in lowercase. However symbols of units after a scientist name has to be in lower case when written full and when abbreviation is being written then it is in uppercase. In this case.( A or ohms/Kohms) "There should not be a period after Uppercase letter."

Ashish Jha
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    I don't think `Kohms` is the correct notation. Can you back your claim with a reference? – Velvel Mar 24 '22 at 07:46
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    '**K**ohms' = **kelvin**-ohms. Capitals matter. 'kOhm' and 'kohm' are wrong. 'kilohm' is correct according to the standards. I think you'll find the information [here](https://www.nist.gov/pml/weights-and-measures/writing-si-metric-system-units#:~:text=NOT%20250%20mms.-,Capitalization,written%20as%2037%20degrees%20Celsius.) when the site is back online. – Transistor Mar 24 '22 at 08:50
  • @Transistor I think you missed an 'o'. kilohm seems like an accidental portmanteau – raaymaan Mar 24 '22 at 08:53
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    @raaymaan, no, it's correct. See Section 9.3 of https://physics.nist.gov/cuu/pdf/sp811.pdf. "*... there are three cases in which the final vowel of an SI prefix is commonly omitted: megohm (not megaohm), kilohm (not kiloohm), and hectare (not hectoare). In all other cases in which the unit name begins with a vowel, both the final vowel of the prefix and the vowel of the unit name are retained and both are pronounced.*" – Transistor Mar 24 '22 at 09:09
  • I didn't know that, thanks for the info! – raaymaan Mar 24 '22 at 10:17