Regarding this, how big should a makeup vanity be?
If space and budget allow, use a built-in vanity. Makeup vanities need a width of only about 30 to 36 inches (76 to 92 centimeters) and a counter height of 30 inches (76 centimeters), which is desk or dining table height. You may want more width if you want extra drawers for this configuration.
In this regard, how deep is a vanity cabinet?
The standard vanity depth is 21 inches. But you can gain floor space in a small bath by trimming at least part of the vanity to 18, 15, or even 12 inches deep.
Further advice for measuring a dressing table space. You will need at least 160 cm of wall height. At a minimum, you need 80 cm for the height of the dresser and 80 cm for the height of a mirror that sits on top of a dresser.