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The max-width CSS descriptor specifies the maximum width of the viewport of a document defined via the @viewport at-rule.

By default, the width is set as close as possible to the initial viewport considering the maximum width constraint.

Related at-rule@viewport
Initial valueauto
Percentagesrefer to the width of the initial viewport
Mediavisual, continuous
Computed valueif specified as a length, the corresponding absolute length; if specified as a percentage, the specified value; otherwise, auto
Canonical orderthe unique non-ambiguous order defined by the formal grammar


/* Keyword value */
max-width auto;

/* <length> values */
max-width: 600px;
max-width: 80em;
max-width: 15cm;

/* <percentage> value */
max-width: 75%;


The used value is calculated from the other CSS descriptors' values.
A non-negative absolute or relative length.
A percentage value relative to the width of the initial viewport at zoom factor 1.0 for horizontal lengths. Must be non-negative.

Formal syntax


<viewport-length> = auto | <length-percentage>

<length-percentage> = <length> | <percentage>


Specification Status Comment
CSS Device Adaptation
The definition of '"max-width" descriptor' in that specification.
Working Draft Initial definition

Browser compatibility

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari
Basic support 29 (behind a flag) No support 10 -ms 11.10
Removed in 15
Reintroduced behind a flag in 16
No support
Feature Android Chrome for Android Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile
Basic support 4.4 29 No support 10-ms 11.10
Removed in 15
Reintroduced behind a flag in 16
No support

Document Tags and Contributors

 Contributors to this page: Sebastianz, mrenty, tuttza
 Last updated by: Sebastianz,