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
Mediaas each of the properties of the shorthand:
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

FeatureChromeEdgeFirefoxInternet ExplorerOperaSafari
Basic support29 ? No10 -ms-


11.1 — 15

FeatureAndroid webviewChrome for AndroidEdge mobileFirefox for AndroidOpera AndroidiOS SafariSamsung Internet
Basic support4.429 ? No


11.1 — 14

No Yes

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Contributors to this page: fscholz, mfluehr, Alhadis, johnsonjo4531, Sebastianz, mrenty, tuttza
Last updated by: fscholz,