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CSS Measurement Units

CSS supports a number of measurements including absolute units such as pixels, inches, centimeters, points, and so on, as well as relative measures such as percentages and em units.

Absolute units

The absolute units are fixed in relation to each other and a length expressed in any of these will appear as exactly that size.

Unit Description Example
px pixels Demo
cm centimeters Demo
mm millimeters Demo
in inches (1in = 2.54cm = 96px) Demo
pt points (1pt = 1/72 of 1in) Demo
pc picas (1pc = 12 pt) Demo

Relative units

A relative unit gets sizing from something else. In the specification the relative length units are defined as em, ex, ch and rem. These are font-relative lengths. The specification also defines a % value, which is always relative to another value.

Using relative values means that things can scale up and down according to some other value.

Unit Description Example
% Relative to the parent element, eg. 200% = 28px if parent element's font-size is 14px Demo
em Relative to the parent element, eg. 2em = 28px if parent element's font-size is 14px Demo
ex Relative to the x-height of the current font Demo
ch Relative to width of the "zero"
rem Relative to font-size of the root element (<html>) Demo
vw Relative to 1% of the width of the viewport (window size) Demo
vh Relative to 1% of the height of the viewport (window size) Demo
vmin Relative to 1% of viewport's smaller dimension Demo
vmax Relative to 1% of viewport's larger dimension Demo