preserveAspectRatio

The preserveAspectRatio attribute indicates how an element with a viewBox providing a given aspect ratio must fit into a viewport with a different aspect ratio.

Because the aspect ratio of an SVG image is defined by the viewBox attribute, if this attribute isn't set, the preserveAspectRatio attribute has no effect (with one exception, the <image> element, as described below).

Example

<svg viewBox="-1 -1 162 92" xmlns="http://www.w3.org/2000/svg">
  <defs>
     <path id="smiley" d="M50,10 A40,40,1,1,1,50,90 A40,40,1,1,1,50,10 M30,40 Q36,35,42,40 M58,40 Q64,35,70,40 M30,60 Q50,75,70,60 Q50,75,30,60" />
  </defs>

  <!-- (width>height) meet -->
  <svg preserveAspectRatio="xMidYMid meet"  x="0"   y="0"  viewBox="0 0 100 100" width="20"  height="10"><use href="#smiley" /></svg>
  <svg preserveAspectRatio="xMinYMid meet"  x="25"  y="0"  viewBox="0 0 100 100" width="20"  height="10"><use href="#smiley" /></svg>
  <svg preserveAspectRatio="xMaxYMid meet"  x="50"  y="0"  viewBox="0 0 100 100" width="20"  height="10"><use href="#smiley" /></svg>

  <!-- (width>height) slice -->
  <svg preserveAspectRatio="xMidYMin slice" x="0"   y="15" viewBox="0 0 100 100" width="20"  height="10"><use href="#smiley" /></svg>
  <svg preserveAspectRatio="xMidYMid slice" x="25"  y="15" viewBox="0 0 100 100" width="20"  height="10"><use href="#smiley" /></svg>
  <svg preserveAspectRatio="xMidYMax slice" x="50"  y="15" viewBox="0 0 100 100" width="20"  height="10"><use href="#smiley" /></svg>

  <!-- (width<height) meet -->
  <svg preserveAspectRatio="xMidYMin meet"  x="75"  y="0"  viewBox="0 0 100 100" width="10"  height="25"><use href="#smiley" /></svg>
  <svg preserveAspectRatio="xMidYMid meet"  x="90"  y="0"  viewBox="0 0 100 100" width="10"  height="25"><use href="#smiley" /></svg>
  <svg preserveAspectRatio="xMidYMax meet"  x="105" y="0"  viewBox="0 0 100 100" width="10"  height="25"><use href="#smiley" /></svg>

  <!-- (width<height) slice -->
  <svg preserveAspectRatio="xMinYMid slice" x="120" y="0"  viewBox="0 0 100 100" width="10"  height="25"><use href="#smiley" /></svg>
  <svg preserveAspectRatio="xMidYMid slice" x="135" y="0"  viewBox="0 0 100 100" width="10"  height="25"><use href="#smiley" /></svg>
  <svg preserveAspectRatio="xMaxYMid slice" x="150" y="0"  viewBox="0 0 100 100" width="10"  height="25"><use href="#smiley" /></svg>

  <!-- none -->
  <svg preserveAspectRatio="none"           x="0"   y="30" viewBox="0 0 100 100" width="160" height="60"><use href="#smiley" /></svg>
</svg>

html,body,svg { height:100% }

<svg viewBox="-1 -1 162 92" xmlns="http://www.w3.org/2000/svg">
  <defs>
     <path id="smiley" d="M50,10 A40,40,1,1,1,50,90 A40,40,1,1,1,50,10 M30,40 Q36,35,42,40 M58,40 Q64,35,70,40 M30,60 Q50,75,70,60 Q50,75,30,60" />
  </defs>

  <!-- (width>height) meet -->
  <rect x="0" y="0" width="20" height="10">
    <title>xMidYMid meet</title>
  </rect>
  <svg viewBox="0 0 100 100" width="20" height="10"
       preserveAspectRatio="xMidYMid meet" x="0" y="0">
    <use href="#smiley" />
  </svg>

  <rect x="25" y="0" width="20" height="10">
    <title>xMinYMid meet</title>
  </rect>
  <svg viewBox="0 0 100 100" width="20" height="10"
       preserveAspectRatio="xMinYMid meet" x="25" y="0">
    <use href="#smiley" />
  </svg>

  <rect x="50" y="0" width="20" height="10">
    <title>xMaxYMid meet</title>
  </rect>
  <svg viewBox="0 0 100 100" width="20" height="10"
       preserveAspectRatio="xMaxYMid meet" x="50" y="0">
    <use href="#smiley" />
  </svg>

  <!-- (width>height) slice -->
  <rect x="0" y="15" width="20" height="10">
    <title>xMidYMin slice</title>
  </rect>
  <svg viewBox="0 0 100 100" width="20" height="10"
       preserveAspectRatio="xMidYMin slice" x="0" y="15">
    <use href="#smiley" />
  </svg>

  <rect x="25" y="15" width="20" height="10">
    <title>xMidYMid slice</title>
  </rect>
  <svg viewBox="0 0 100 100" width="20" height="10"
       preserveAspectRatio="xMidYMid slice" x="25" y="15">
    <use href="#smiley" />
  </svg>

  <rect x="50" y="15" width="20" height="10">
    <title>xMidYMax slice</title>
  </rect>
  <svg viewBox="0 0 100 100" width="20" height="10"
       preserveAspectRatio="xMidYMax slice" x="50" y="15">
    <use href="#smiley" />
  </svg>

  <!-- (width<height) meet -->
  <rect x="75" y="0" width="10" height="25">
    <title>xMidYMin meet</title>
  </rect>
  <svg viewBox="0 0 100 100" width="10" height="25"
       preserveAspectRatio="xMidYMin meet" x="75" y="0">
    <use href="#smiley" />
  </svg>

  <rect x="90" y="0" width="10" height="25">
    <title>xMidYMid meet</title>
  </rect>
  <svg viewBox="0 0 100 100" width="10" height="25"
       preserveAspectRatio="xMidYMid meet" x="90" y="0">
    <use href="#smiley" />
  </svg>

  <rect x="105" y="0" width="10" height="25">
    <title>xMidYMax meet</title>
  </rect>
  <svg viewBox="0 0 100 100" width="10" height="25"
       preserveAspectRatio="xMidYMax meet" x="105" y="0">
    <use href="#smiley" />
  </svg>

  <!-- (width<height) slice -->
  <rect x="120" y="0" width="10" height="25">
    <title>xMinYMid slice</title>
  </rect>
  <svg viewBox="0 0 100 100" width="10" height="25"
       preserveAspectRatio="xMinYMid slice" x="120" y="0">
    <use href="#smiley" />
  </svg>

  <rect x="135" y="0" width="10" height="25">
    <title>xMidYMid slice</title>
  </rect>
  <svg viewBox="0 0 100 100" width="10" height="25"
       preserveAspectRatio="xMidYMid slice" x="135" y="0">
    <use href="#smiley" />
  </svg>

  <rect x="150" y="0" width="10" height="25">
    <title>xMaxYMid slice</title>
  </rect>
  <svg viewBox="0 0 100 100" width="10" height="25"
       preserveAspectRatio="xMaxYMid slice" x="150" y="0">
    <use href="#smiley" />
  </svg>

  <!-- none -->
  <rect x="0" y="30" width="160" height="60">
    <title>none</title>
  </rect>
  <svg viewBox="0 0 100 100" width="160" height="60"
       preserveAspectRatio="none" x="0" y="30">
    <use href="#smiley" />
  </svg>
</svg>

path {
  fill: yellow;
  stroke: black;
  stroke-width: 8px;
  stroke-linecap: round;
  stroke-linejoin: round;
  pointer-events: none;
}

rect:hover, rect:active {
  outline: 1px solid red;
}

Syntax

preserveAspectRatio="<align> [<meetOrSlice>]"

Its value is made of one or two keywords: A required alignment value and an optional "meet or slice" reference as described below:

Alignment value

The alignment value indicates whether to force uniform scaling and, if so, the alignment method to use in case the aspect ratio of the viewBox doesn't match the aspect ratio of the viewport. The alignment value must be one of the following keywords:

• none
  Do not force uniform scaling. Scale the graphic content of the given element non-uniformly if necessary such that the element's bounding box exactly matches the viewport rectangle. Note that if <align> is none, then the optional <meetOrSlice> value is ignored.
• xMinYMin - Force uniform scaling.
  Align the <min-x> of the element's viewBox with the smallest X value of the viewport.
  Align the <min-y> of the element's viewBox with the smallest Y value of the viewport.
• xMidYMin - Force uniform scaling.
  Align the midpoint X value of the element's viewBox with the midpoint X value of the viewport.
  Align the <min-y> of the element's viewBox with the smallest Y value of the viewport.
• xMaxYMin - Force uniform scaling.
  Align the <min-x>+<width> of the element's viewBox with the maximum X value of the viewport.
  Align the <min-y> of the element's viewBox with the smallest Y value of the viewport.
• xMinYMid - Force uniform scaling.
  Align the <min-x> of the element's viewBox with the smallest X value of the viewport.
  Align the midpoint Y value of the element's viewBox with the midpoint Y value of the viewport.
• xMidYMid (the default) - Force uniform scaling.
  Align the midpoint X value of the element's viewBox with the midpoint X value of the viewport.
  Align the midpoint Y value of the element's viewBox with the midpoint Y value of the viewport.
• xMaxYMid - Force uniform scaling.
  Align the <min-x>+<width> of the element's viewBox with the maximum X value of the viewport.
  Align the midpoint Y value of the element's viewBox with the midpoint Y value of the viewport.
• xMinYMax - Force uniform scaling.
  Align the <min-x> of the element's viewBox with the smallest X value of the viewport.
  Align the <min-y>+<height> of the element's viewBox with the maximum Y value of the viewport.
• xMidYMax - Force uniform scaling.
  Align the midpoint X value of the element's viewBox with the midpoint X value of the viewport.
  Align the <min-y>+<height> of the element's viewBox with the maximum Y value of the viewport.
• xMaxYMax - Force uniform scaling.
  Align the <min-x>+<width> of the element's viewBox with the maximum X value of the viewport.
  Align the <min-y>+<height> of the element's viewBox with the maximum Y value of the viewport.

Meet or slice reference

The meet or slice reference is optional and, if provided, must be one of the following keywords:

• meet (the default) - Scale the graphic such that:
  • aspect ratio is preserved
  • the entire viewBox is visible within the viewport
  • the viewBox is scaled up as much as possible, while still meeting the other criteria
  In this case, if the aspect ratio of the graphic does not match the viewport, some of the viewport will extend beyond the bounds of the viewBox (i.e., the area into which the viewBox will draw will be smaller than the viewport).
• slice - Scale the graphic such that:
  • aspect ratio is preserved
  • the entire viewport is covered by the viewBox
  • the viewBox is scaled down as much as possible, while still meeting the other criteria
  In this case, if the aspect ratio of the viewBox does not match the viewport, some of the viewBox will extend beyond the bounds of the viewport (i.e., the area into which the viewBox will draw is larger than the viewport).

Elements

Seven elements are using this attribute: <svg>, <symbol>, <image>, <feImage>, <marker>, <pattern>, and <view>.

feImage

For <feImage>, preserveAspectRatio defines how the referenced image should fit in the rectangle define by the <feImage> element.

image

For <image>, preserveAspectRatio defines how the referenced image should fit in the rectangle define by the <image> element.

marker

For <marker>, preserveAspectRatio indicates if a uniform scaling must be performed to fit the element viewport.

pattern

For <pattern>, preserveAspectRatio indicates if a uniform scaling must be performed to fit the element viewport.

svg

For <svg>, preserveAspectRatio indicates if a uniform scaling must be performed to fit the element viewport.

symbol

For <symbol>, preserveAspectRatio indicates if a uniform scaling must be performed to fit the element viewport.

view

For <view>, preserveAspectRatio indicates if a uniform scaling must be performed to fit the element viewport.

Specification