Infinity symbol with HTML

∞

This does not require a HTML entity if you are using a modern encoding (such as UTF-8). And if you're not already, you probably should be.

Use the HTML entity ∞ or ∞.

You can use the following:

• literal: ∞ (if the encoding you use can encode it — UTF-8 can, for example)
• character reference: ∞ (decimal), ∞ (hexadecimal)
• entity reference: ∞

But whether it is displayed correctly does also depend on the font the text is displayed with.