What ≈ means
The sign ≈ reads "is approximately equal to". It says two values are close but not exactly the same, usually because one of them has been rounded: π ≈ 3.14, 1/3 ≈ 0.333 and √2 ≈ 1.414.
You will also see ≈ outside math as a short way to write "about": a trip of ≈ 20 minutes, or a file of ≈ 3 MB. For values that are exactly equal, use = instead, and for values that differ, use the not equal symbol ≠.
Which approximately sign should you use?
≈ is the safe default for rounded numbers. ~ (tilde) is the casual version ("~5 min"), and in math the tilde operator ∼ often means "is similar to" or "has the same order of magnitude as".
≃ means "asymptotically equal" and in some fields marks an isomorphism. ≅ is officially named "approximately equal to" in Unicode, but in geometry it means congruent (△ABC ≅ △DEF). ≒ is common in Japan, where it is often used in place of ≈. ∝ looks related but means "is proportional to".
How to type the approximate sign on a keyboard
There is no ≈ key, but every system has a way. On a Mac, press Option + X. On Windows, hold Alt and type 247 on the number pad. In Microsoft Word, type 2248 and press Alt + X. In Google Docs, use Insert > Special characters and search for "almost equal".
In LaTeX, use \approx, plus \sim, \simeq and \cong for the other signs. In HTML, write ≈. On phones, copy ≈ from this page or set up a text replacement. For tolerances such as 5 ± 0.1, use the plus minus symbol instead.