There are 44 CSS length units
Adam Argyle has written a Codepen that lists the different units.
To learn more about what each unit means:
Relative
| Unit |
Definition |
| % |
Percentage of the parent element's font size |
| em |
Font size of the element |
| ex |
Height of the element's font |
| ch |
Width of the "0" (zero) character of the element's font |
| cap |
Hight of the capital letters of the element's font |
| ic |
Advance measure of the 水 CJK (Chinese/Japanese/Korean) character of the element's font |
| lh |
Height of the element's line height |
Root Relative
| Unit |
Definition |
| rem |
Font size of the root element |
| rex |
Height of the root element's font |
| rch |
Width of the "0" (zero) character of the root element's font |
| rlh |
Height of the root element's line height |
| ric |
Advance measure of the 水 CJK (Chinese/Japanese/Korean) character of the root element's font |
| rcap |
Height of the capital letters of the root element's font |
Absolute
| Unit |
Definition |
| px |
Pixels |
| pt |
Points |
| pc |
Picas |
| in |
Inches |
| cm |
Centimeters |
| mm |
Millimeters |
| Q |
Quarter-millimeters |
Viewport
| Unit |
Definition |
| vw |
Viewport width |
| vh |
Viewport height |
| vi |
Viewport inches |
| vb |
Viewport breadths |
| dvw |
Dynamic viewport width |
| dvh |
Dynamic viewport height |
| dvi |
Dynamic viewport inches |
| dvb |
Dynamic viewport breadths |
| svw |
Smallest possible viewport width |
| svh |
Smallest possible viewport height |
| svi |
Smallest possible viewport inches |
| svb |
Smallest possible viewport breadths |
| lvw |
Largest possible viewport width |
| lvh |
Largest possible viewport height |
| lvi |
Largest possible viewport inches |
| lvb |
Largest possible viewport breadths |
| vmin |
Smallest value between the viewport's width and height |
| vmax |
Largest value between the viewport's width and height |
Container
See CSS Container Queries.
| Unit |
Definition |
| cqw |
Container width |
| cqh |
Container height |
| cqi |
Container inches |
| cqb |
Container breadths |
| cqmin |
Smallest value between the element's parent container's width and height |
| cqmax |
Largests value between the element's parent container's width and height |