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align-content align-items align-self all animation animation-delay animation-direction animation-duration animation-fill-mode animation-iteration-count animation-name animation-play-state animation-timing-function backface-visibility background background-attachment background-blend-mode background-clip background-color background-image background-origin background-position background-repeat background-size border border-bottom border-bottom-color border-bottom-left-radius border-bottom-right-radius border-bottom-style border-bottom-width border-collapse border-color border-image border-image-outset border-image-repeat border-image-slice border-image-source border-image-width border-left border-left-color border-left-style border-left-width border-radius border-right border-right-color border-right-style border-right-width border-spacing border-style border-top border-top-color border-top-left-radius border-top-right-radius border-top-style border-top-width border-width bottom box-decoration-break box-shadow box-sizing break-after break-before break-inside caption-side caret-color @charset clear clip clip-path color column-count column-fill column-gap column-rule column-rule-color column-rule-style column-rule-width column-span column-width columns content counter-increment counter-reset cursor direction display empty-cells filter flex flex-basis flex-direction flex-flow flex-grow flex-shrink flex-wrap float font @font-face font-family font-feature-settings font-kerning font-size font-size-adjust font-stretch font-style font-variant font-variant-caps font-weight gap grid grid-area grid-auto-columns grid-auto-flow grid-auto-rows grid-column grid-column-end grid-column-gap grid-column-start grid-gap grid-row grid-row-end grid-row-gap grid-row-start grid-template grid-template-areas grid-template-columns grid-template-rows hanging-punctuation height hyphens @import isolation justify-content @keyframes left letter-spacing line-height list-style list-style-image list-style-position list-style-type margin margin-bottom margin-left margin-right margin-top max-height max-width @media min-height min-width mix-blend-mode object-fit object-position opacity order outline outline-color outline-offset outline-style outline-width overflow overflow-x overflow-y padding padding-bottom padding-left padding-right padding-top page-break-after page-break-before page-break-inside perspective perspective-origin pointer-events position quotes resize right row-gap scroll-behavior tab-size table-layout text-align text-align-last text-decoration text-decoration-color text-decoration-line text-decoration-style text-indent text-justify text-overflow text-shadow text-transform top transform transform-origin transform-style transition transition-delay transition-duration transition-property transition-timing-function unicode-bidi user-select vertical-align visibility white-space width word-break word-spacing word-wrap writing-mode z-index



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.

Example

Set different length values, using px (pixels):

h1 {
  font-size: 60px;
}

p {
  font-size: 25px;
  line-height: 50px;
}

Try it Yourself »

Note: 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 Try it
mm millimeters Try it
in inches (1in = 96px = 2.54cm) Try it
px * pixels (1px = 1/96th of 1in) Try it
pt points (1pt = 1/72 of 1in) Try it
pc picas (1pc = 12 pt) Try it

* 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 scale better between different rendering medium.

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

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 12.0 19.0 6.0 20.0
vmax 26.0 16.0 19.0 7.0 20.0