CSS Units
CSS Units
CSS has several different units for expressing a length.
Many CSS properties take "length" values, such as width, margin, padding,
font-size, etc.
Example
Set different length values with px and em:
h1 {
font-size: 60px;
}
p {
font-size: 1.5em;
line-height: 2em;
}
The length value is a number followed by a length unit, such as
px, em, rem, etc.
Note: A whitespace cannot appear between the number and the unit. However, if the value is
0, the unit can be omitted.
Two Types of Length Units
CSS has two types of length units:
- Absolute units - Fixed sizes that do not change
- Relative units - Sizes relative to another length (parent, root, or viewport)
Absolute Units
Absolute units are fixed, and the length expressed in any of these will appear exactly that size.
The most used absolute unit is px (pixels).
Absolute units are not recommended for screens, because screen sizes vary so much. However, they can be used if the output medium is known, such as for print layout.
| Unit | Description |
|---|---|
| px | pixels (1px = 1/96th of 1in) |
| pt | points (1pt = 1/72 of 1in) |
| cm, mm, in, pc | centimeters, millimeters, inches, picas |
Learn more about Absolute Units »
Relative Units
Relative units specify a length relative to another length (like parent element, root element, or viewport).
Relative length units scale better between different screen sizes, making them ideal for responsive web design.
| Unit | Description |
|---|---|
| em | Relative to the font-size of the parent element |
| rem | Relative to the font-size of the root element |
| vw, vh | Relative to 1% of the viewport width/height |
| % | Relative to the size of the parent element |
Tip: The em and
rem units are perfect for creating
scalable and responsive websites!
Learn more about Relative Units »
