It equals the height of — not surprisingly— the letter “x”.
Optical Effects in User Interfaces (for True Nerds)
Slava Shestopalov
61K148

Nitpick: no. As you said, it’s “the height of a lowercase letter of a font”. Period. The letter “x” itself may be smaller or taller than the x-height.

One clap, two clap, three clap, forty?

By clapping more or less, you can signal to us which stories really stand out.