google-fonts/cc-by-sa/knowledge/glossary/terms/optical_sizes/content.md

Optical sizes are different versions of a typeface optimized for use at specific sizes or size ranges.


On the left, text set in four different optical sizes—display, subhead, body, and caption—at the intended font sizes for each. On the right, all set at the same font size.

Small (or body) optical sizes tend to have:

• less stroke contrast,
• more open spacing,
• and taller x-heights

than those of their large (or display) counterparts. Different optical sizes can be split into separate font files or be assigned to the optical size axis within a variable font.