CSS Length Units

Length units in CSS fall under two categories: relative units and absolute units.

Relative units include:

px: pixels

em: em

ex: height of letter x

Absolute units include:

in: inches

cm: centimeters

mm: millimeters

pt: points, 1 pt = 1/72 in

pc: picas, 1 pc = 12 pt

If no unit is specified, the default unit is px.

Below are examples for each unit type:

CSS Declaration Output

p {font-size:9px;}
Font Size 9px.

p {font-size:3em;}

Font Size 3em.

p {font-size:3ex;}

Font Size 3ex.

p {font-size:0.2in;}

Font Size 0.2 inch.

p {font-size:0.5cm;}

Font Size 0.5 cm.

p {font-size:12mm;}

Font Size 12 mm.

p {font-size:24pt;}

Font Size 24 pt.

p {font-size:2pc;}

Font Size 2 pc.

The general recommendation is to use relative length units. This way, you allow the users to increase or decrease the font size as they please. Using absolute length units takes away this option.

Next: CSS Box Model

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