Omega (ω) in HTML
Omega is the twenty fourth and last Greek letter, written Ω and ω. The capital is at U+03A9 and the small letter at U+03C9.
At a glance
- Character
- Ω ω
- Named entity
- Ω ω
- Decimal reference
- Ω ω
- Hex reference
- Ω ω
- Unicode code point
- U+03A9, U+03C9
- Unicode name
- GREEK CAPITAL LETTER OMEGA, GREEK SMALL LETTER OMEGA
- In the entity reference
- Greek
In detail
The capital omega is the symbol for the ohm, the unit of electrical resistance, and this is the second place in Unicode where a Greek letter has a duplicate. The ohm sign at U+2126 was encoded separately for compatibility with older standards, and it has a canonical decomposition to the Greek capital letter, which means the standard normalisation forms convert it. Use the Greek letter: the ohm sign is a character you should expect to be normalised away.
In physics the small omega is angular frequency, measured in radians per second, and it is two pi times the ordinary frequency in cycles per second. Confusing the two is a factor of about six error, and it is common enough that quantities are usually labelled with the unit rather than trusting the symbol to disambiguate.
In complexity analysis the capital omega is the counterpart of big O: a lower bound on the growth of a function, where big O is an upper bound and big theta is both. The three form a set, and a claim written with the wrong one of them says something the author usually did not intend.
Because it is the last letter of the alphabet, omega is used idiomatically for an end state or a limit, which is where the phrase alpha and omega comes from. That is a literary use rather than a notational one and the Greek characters are rarely the right way to write it.
Examples
<p>R = 4.7 kΩ</p>
<p>ω = 2πf, so 50 Hz is about 314 rad/s.</p>const ohmSign = "\u2126"; // OHM SIGN
const greek = "\u03A9"; // GREEK CAPITAL LETTER OMEGA
ohmSign === greek; // false
ohmSign.normalize("NFC") === greek; // trueThings that catch people out
- The ohm sign is decomposed by standard normalisation, so a value stored with it may come back as the Greek letter and fail a byte comparison against the original.
- Angular frequency and ordinary frequency differ by a factor of two pi. Always carry the unit.
- Big O, big omega and big theta are three different claims. Only big theta asserts the bound is tight.
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Related HTML entities
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