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<!DOCTYPE html><html lang="en"><head><meta charSet="utf-8"/><meta http-equiv="X-UA-Compatible" content="IE=edge"/><title>PixelRatio · React Native</title><meta name="viewport" content="width=device-width"/><meta name="generator" content="Docusaurus"/><meta name="description" content="<p>PixelRatio class gives access to the device pixel density.</p>
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</script></nav></div><div class="container mainContainer"><div class="wrapper"><div class="post"><header class="postHeader"><a class="edit-page-link button" href="https://github.com/facebook/react-native-website/blob/master/docs/pixelratio.md" target="_blank" rel="noreferrer noopener">Edit</a><h1 class="postHeaderTitle">PixelRatio</h1></header><article><div><span><p>PixelRatio class gives access to the device pixel density.</p>
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<h3><a class="anchor" aria-hidden="true" id="fetching-a-correctly-sized-image"></a><a href="#fetching-a-correctly-sized-image" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Fetching a correctly sized image</h3>
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<p>You should get a higher resolution image if you are on a high pixel density device. A good rule of thumb is to multiply the size of the image you display by the pixel ratio.</p>
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<pre><code class="hljs"><span class="hljs-built_in">var</span> <span class="hljs-built_in">image</span> = getImage({
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<span class="hljs-built_in">width</span>: PixelRatio.getPixelSizeForLayoutSize(<span class="hljs-number">200</span>),
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<span class="hljs-built_in">height</span>: PixelRatio.getPixelSizeForLayoutSize(<span class="hljs-number">100</span>),
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});
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<Image source={<span class="hljs-built_in">image</span>} <span class="hljs-built_in">style</span>={{<span class="hljs-built_in">width</span>: <span class="hljs-number">200</span>, <span class="hljs-built_in">height</span>: <span class="hljs-number">100</span>}} />
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</code></pre>
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<h3><a class="anchor" aria-hidden="true" id="methods"></a><a href="#methods" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Methods</h3>
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<ul>
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<li><a href="/react-native/docs/0.21/pixelratio#get"><code>get</code></a></li>
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<li><a href="/react-native/docs/0.21/pixelratio#getfontscale"><code>getFontScale</code></a></li>
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<li><a href="/react-native/docs/0.21/pixelratio#getpixelsizeforlayoutsize"><code>getPixelSizeForLayoutSize</code></a></li>
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<li><a href="/react-native/docs/0.21/pixelratio#roundtonearestpixel"><code>roundToNearestPixel</code></a></li>
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<li><a href="/react-native/docs/0.21/pixelratio#startdetecting"><code>startDetecting</code></a></li>
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</ul>
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<hr>
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<h1><a class="anchor" aria-hidden="true" id="reference"></a><a href="#reference" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Reference</h1>
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<h2><a class="anchor" aria-hidden="true" id="methods-1"></a><a href="#methods-1" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Methods</h2>
|
||
<h3><a class="anchor" aria-hidden="true" id="get"></a><a href="#get" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a><code>get()</code></h3>
|
||
<pre><code class="hljs css language-javascript"><span class="token keyword">static</span> <span class="token keyword">get</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
|
||
</code></pre>
|
||
<p>Returns the device pixel density. Some examples:</p>
|
||
<ul>
|
||
<li>PixelRatio.get() === 1
|
||
<ul>
|
||
<li><a href="https://material.io/tools/devices/">mdpi Android devices</a></li>
|
||
</ul></li>
|
||
<li>PixelRatio.get() === 1.5
|
||
<ul>
|
||
<li><a href="https://material.io/tools/devices/">hdpi Android devices</a></li>
|
||
</ul></li>
|
||
<li>PixelRatio.get() === 2
|
||
<ul>
|
||
<li>iPhone 4, 4S</li>
|
||
<li>iPhone 5, 5c, 5s</li>
|
||
<li>iPhone 6, 7, 8</li>
|
||
<li><a href="https://material.io/tools/devices/">xhdpi Android devices</a></li>
|
||
</ul></li>
|
||
<li>PixelRatio.get() === 3
|
||
<ul>
|
||
<li>iPhone 6 Plus, 7 Plus, 8 Plus</li>
|
||
<li>iPhone X</li>
|
||
<li>Pixel, Pixel 2</li>
|
||
<li><a href="https://material.io/tools/devices/">xxhdpi Android devices</a></li>
|
||
</ul></li>
|
||
<li>PixelRatio.get() === 3.5
|
||
<ul>
|
||
<li>Nexus 6</li>
|
||
<li>Pixel XL, Pixel 2 XL</li>
|
||
<li><a href="https://material.io/tools/devices/">xxxhdpi Android devices</a></li>
|
||
</ul></li>
|
||
</ul>
|
||
<hr>
|
||
<h3><a class="anchor" aria-hidden="true" id="getfontscale"></a><a href="#getfontscale" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a><code>getFontScale()</code></h3>
|
||
<pre><code class="hljs css language-javascript"><span class="token keyword">static</span> <span class="token function">getFontScale</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
|
||
</code></pre>
|
||
<p>Returns the scaling factor for font sizes. This is the ratio that is used to calculate the absolute font size, so any elements that heavily depend on that should use this to do calculations.</p>
|
||
<p>If a font scale is not set, this returns the device pixel ratio.</p>
|
||
<p>Currently this is only implemented on Android and reflects the user preference set in Settings > Display > Font size, on iOS it will always return the default pixel ratio. @platform android</p>
|
||
<hr>
|
||
<h3><a class="anchor" aria-hidden="true" id="getpixelsizeforlayoutsize"></a><a href="#getpixelsizeforlayoutsize" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a><code>getPixelSizeForLayoutSize()</code></h3>
|
||
<pre><code class="hljs css language-javascript"><span class="token keyword">static</span> <span class="token function">getPixelSizeForLayoutSize</span><span class="token punctuation">(</span>layoutSize<span class="token punctuation">)</span>
|
||
</code></pre>
|
||
<p>Converts a layout size (dp) to pixel size (px).</p>
|
||
<p>Guaranteed to return an integer number.</p>
|
||
<hr>
|
||
<h3><a class="anchor" aria-hidden="true" id="roundtonearestpixel"></a><a href="#roundtonearestpixel" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a><code>roundToNearestPixel()</code></h3>
|
||
<pre><code class="hljs css language-javascript"><span class="token keyword">static</span> <span class="token function">roundToNearestPixel</span><span class="token punctuation">(</span>layoutSize<span class="token punctuation">)</span>
|
||
</code></pre>
|
||
<p>Rounds a layout size (dp) to the nearest layout size that corresponds to an integer number of pixels. For example, on a device with a PixelRatio of 3, <code>PixelRatio.roundToNearestPixel(8.4) = 8.33</code>, which corresponds to exactly (8.33 * 3) = 25 pixels.</p>
|
||
<hr>
|
||
<h3><a class="anchor" aria-hidden="true" id="startdetecting"></a><a href="#startdetecting" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a><code>startDetecting()</code></h3>
|
||
<pre><code class="hljs css language-javascript"><span class="token keyword">static</span> <span class="token function">startDetecting</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
|
||
</code></pre>
|
||
<p>// No-op for iOS, but used on the web. Should not be documented.</p>
|
||
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