The Speed Coding

CSS Tutorial

CSS Introduction CSS Syntax CSS Selectors CSS How To CSS Comments CSS Colors CSS Backgrounds CSS Borders CSS Margins CSS Padding CSS Height/Width CSS Box Model CSS Outline CSS Text CSS Fonts CSS Icons CSS Links CSS Lists CSS Tables CSS Display CSS Max-width CSS Position CSS Overflow CSS Float CSS Inline-block CSS Align CSS Combinators CSS Pseudo-class CSS Pseudo-element CSS Opacity CSS Navigation Bar CSS Dropdowns CSS Image Gallery CSS Image Sprites CSS Attr Selectors CSS Forms CSS Counters CSS Website Layout CSS Units CSS Specificity

CSS Advanced

CSS Rounded Corners CSS Border Images CSS Backgrounds CSS Colors CSS Gradients CSS Shadows CSS Text Effects CSS Web Fonts CSS 2D Transforms CSS 3D Transforms CSS Transitions CSS Animations CSS Tooltips CSS Style Images CSS object-fit CSS Buttons CSS Pagination CSS Multiple Columns CSS User Interface CSS Variables CSS Box Sizing CSS Flexbox CSS Media Queries CSS MQ Examples

CSS Responsive

RWD Intro RWD Viewport RWD Grid View RWD Media Queries RWD Images RWD Videos RWD Frameworks RWD Templates

CSS Grid

Grid Intro Grid Container Grid Item

CSS References

CSS Reference CSS Selectors CSS Functions CSS Reference Aural CSS Web Safe Fonts CSS Animatable CSS Units CSS Colors CSS Color Values CSS Default Values CSS Browser Support

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.

Length is a number followed by a length unit, such as 10px, 2em, etc.

A whitespace cannot appear between the number and the unit. However, if the value is 0, the unit can be omitted.

For some CSS properties, negative lengths are allowed.

There are two types of length units: absolute and relative.


Absolute Lengths

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

Absolute length units are not recommended for use on screen, because screen sizes vary so much. However, they can be used if the output medium is known, such as for print layout.

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

* Pixels (px) are relative to the viewing device. For low-dpi devices, 1px is one device pixel (dot) of the display. For printers and high resolution screens 1px implies multiple device pixels.


Relative Lengths

Relative length units specify a length relative to another length property. Relative length units scales better between different rendering mediums.

Unit Description
em Relative to the font-size of the element (2em means 2 times the size of the current font)
ex Relative to the x-height of the current font (rarely used)
ch Relative to width of the "0" (zero)
rem Relative to font-size of the root element
vw Relative to 1% of the width of the viewport*
vh Relative to 1% of the height of the viewport*
vmin Relative to 1% of viewport's* smaller dimension
vmax Relative to 1% of viewport's* larger dimension
% Relative to the parent element

Tip: The em and rem units are practical in creating perfectly scalable layout!
* Viewport = the browser window size. If the viewport is 50cm wide, 1vw = 0.5cm.


Browser Support

The numbers in the table specify the first browser version that fully supports the length unit.

Length Unit
em, ex, %, px, cm, mm, in, pt, pc 1.0 3.0 1.0 1.0 3.5
ch 27.0 9.0 1.0 7.0 20.0
rem 4.0 9.0 3.6 4.1 11.6
vh, vw 20.0 9.0 19.0 6.0 20.0
vmin 20.0 9.0* 19.0 6.0 20.0
vmax 26.0 Not supported 19.0 7.0 20.0

Note: Internet Explorer 9 supports vmin with the non-standard name: vm.