Omega symbol Ω

• Ohms: the SI unit of electrical resistance. 220 Ω, 4.7 kΩ, 1 MΩ, with a space between the number and the unit.
• The end: as the last Greek letter, omega stands for the end of something, as in “the Alpha and the Omega,” the beginning and the end.
• Computer science: Ω(n) describes a lower bound on an algorithm’s running time, alongside big O for upper bounds and Θ for tight bounds.
• Math and physics: Ω also names the sample space in probability and solid angles in geometry.

Lowercase ω is common too, especially for angular velocity and angular frequency in physics, measured in radians per second.

Unicode also has a separate ohm sign (U+2126), inherited from older character sets. It is canonically equivalent to the Greek capital omega (U+03A9), so text normalization turns it into omega, and Unicode recommends using the Greek letter even when you mean ohms. The character on this page is the Greek capital omega, the right choice for both uses.

℧ (mho) is an upside-down omega. Mho was the old name for the unit of conductance, the reciprocal of the ohm; the SI unit today is the siemens (S).

In simple sans-serif fonts, Ω can resemble ∩ (intersection) or a horseshoe-shaped dingbat. Copy the exact character when it matters.

• Word: in an equation (Alt+=), type \Omega and press space; lowercase is \omega.
• LaTeX: \Omega in math mode, or with siunitx, \SI{10}{\kilo\ohm} for 10 kΩ.
• Plain-text parts lists: engineers often write 10k or 4R7 (4.7 Ω) when Ω isn’t available; the R marks the decimal point.
• Windows emoji panel: press Windows key + period. The Symbols tab is the one marked with an Ω icon.
• Phones: add the Greek keyboard, or copy Ω here and save a text replacement.