Ohm Sign Ω vs Greek Omega Ω: Which Character Should You Use?

Search a character picker for “ohm” and you may find both Ω and Ω. They usually render the same, but only the second is the ordinary Greek capital omega that Unicode prefers for modern text—and it is also the character used for the SI symbol of the ohm.

The misleading part is the name OHM SIGN attached to U+2126. In current measurement notation, that legacy name is not a recommendation to type the special code point.

The two omega-shaped characters

Why there are two omega-shaped code points

Unicode had to support text from older standards that already contained a dedicated ohm character. U+2126 was retained so legacy material could be represented and converted faithfully.

At the same time, Unicode defined U+2126 as canonically equivalent to U+03A9. The Names List explicitly gives Greek capital omega as the preferred representation. In other words, the older code point remains valid Unicode, but it is not the character Unicode recommends for newly authored text.

Why normalization collapses Ω to Ω

The two forms do not merely happen to look alike. Their equivalence is built into Unicode normalization. A canonical normalization process can replace Ω with Ω while preserving the normalized text meaning.

A raw-code-point comparison can therefore distinguish strings that canonical normalization treats as the same. If an archive needs the original encoding, keep the source text; for ordinary search, matching, and current publishing, normalized Ω is usually more useful.

Writing the ohm in measurements

The SI derived unit of electrical resistance is the ohm, with symbol Ω. A resistance of ten ohms is written 10 Ω. When an SI prefix is used, the prefix joins directly to the unit symbol: 10 kΩ for ten kiloohms or 2 MΩ for two megaohms.

The examples show both spacing rules at once: 10 Ω has a gap before the unit, while 10 kΩ keeps k attached to Ω. Case carries its own meaning too—kilo is k, while mega is M.

Like other unit symbols, Ω is not pluralized. The symbol stays the same in 1 Ω and 10 Ω, even though the written unit name changes from “ohm” to “ohms” in ordinary English prose. A unit symbol is also not followed by a period unless normal sentence punctuation requires one.

Ω is still the Greek letter omega

U+03A9 remains GREEK CAPITAL LETTER OMEGA at the character level. Its role comes from context. In a Greek word it is a letter; in 10 Ω it functions as the unit symbol for ohm; in mathematics it may be used for other conventional meanings.

Unicode does not need a separate modern character for every specialized scientific role of a letter. The same principle explains why ordinary K, rather than a special Kelvin character, is used for the kelvin.

U+2126 still turns up in old documents, character palettes, OCR output, and converted datasets. Because fonts often draw it exactly like Ω, the legacy code point can survive for years without anyone noticing.

If normalization changes Ω to Ω, that is expected Unicode behavior. Only an application that cares about exact source provenance needs to preserve the original code point separately.

A Unicode name is not a usage recommendation

The label OHM SIGN makes U+2126 look like the obvious choice, but Unicode names are permanent identifiers. Some preserve the history of older encodings long after the preferred representation has moved elsewhere.

The same historical pattern appears with Kelvin Sign K vs K and Angstrom Sign Å vs Å: the special letterlike character remains encoded, but regular letters are preferred in modern text.

Watch the case: Ω is not ω

The ohm symbol uses capital omega Ω, U+03A9. Lowercase omega ω, U+03C9, is a different Greek letter character and is widely used for other scientific quantities, including angular frequency in many formulas.

Changing case is therefore not harmless. 10 Ω is a resistance value, while replacing Ω with ω produces a different character with a different conventional role. Technical text should not be passed through generic lowercase or uppercase transformations.

A font may draw omega with different stroke weight, width, or serif details, but those visual choices do not require a different Unicode code point. For modern ohm notation, the underlying character remains U+03A9 even when the surrounding document uses a specialized scientific typeface.

What to type today

For newly written text, use Ω U+03A9. Keep Ω U+2126 only when reproducing or archiving source material where the original encoding itself matters.

For software, the safest rule is simple: recognize both on input, normalize them consistently for search or comparison, and do not depend on the glyph to reveal which code point was stored.