<resolution>

Summary

The <resolution> CSS data types, used in media queries, denotes the density of pixels of an output device, its resolution. It is a <number> immediately followed by a unit of resolution (dpi, dpcm, ...). Like for any CSS dimension, there is no space between the unit literal and the number.

On screens, the length related to CSS inches, centimeters or pixels, not on physical values.

Even if all units represent the same resolution for the value 0, the unit may not be omitted in that case as it isn't a <length>: 0 is invalid and does not represent 0dpi, 0dpcm, nor 0dppx.

Units

dpi
This unit represents the number of dots per inch. A screen typically contains 72 or 96 dpi; a printed document usually reach much greater dpi. As 1 inch is 2.54 cm, 1dpi ≈ 0.39dpcm.
dpcm
This unit represents the number of dots per centimeter. As 1 inch is 2.54 cm, 1dpcm ≈ 2.54dpi.
dppx
This unit represents the number of dots per px unit. Due to the 1:96 fixed ratio of CSS in to CSS px, 1dppx is equivalent to 96dpi, that corresponds to the default resolution of images displayed in CSS as defined by image-resolution.

Examples

Here are some correct uses of <resolution> values:

96dpi                                              Correct use: a <number> (here an <integer>) followed by the unit.
@media print and (min-resolution: 300dpi) { ... }  Correct use in the context of a media query.

Here are some incorrect uses:

72 dpi                                             Incorrect: no spaces allowed between the <number> and the unit.
ten dpi                                            Incorrect: only digits must be used.
0                                                  Incorrect: the unit can be omitted for 0 values only for <length>.

Specifications

Specification Status Comment
CSS Values and Units Module Level 3 Candidate Recommendation Factorization of the type in a more generic specification. No change
CSS Image Values and Replaced Content Module Level 3 Candidate Recommendation Added the dppx unit
Media Queries Recommendation Initial definition

Browser compatibility

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari (WebKit)
Basic support 29 3.5 (1.9.1) [**] 9 9.5 Not supported [*]
dppx 29 16.0 (16.0) ? 12.10 ?
Feature Android Firefox Mobile (Gecko) IE Phone Opera Mobile Safari Mobile
Basic support Not supported [*] yes ? yes Not supported [*]
dppx ? 16.0 (16.0) ? 12.10 ?

[*] Webkit engine does not support CSS resolution query as in the specification, the use of the non-standard device-pixel-ratio query is needed for browsers Safari, see bug 16832.

[**] Before Firefox 8 (Gecko 8.0), it erroneously accepted only CSS dimensions that were <integer> followed by the unit. From that version, it supports any valid CSS dimensions (<number> immediately followed by the unit).

See also

Document Tags and Contributors

Last updated by: paul.gaske,
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