The contentRect read-only property of the ResizeObserverEntry interface returns a DOMRectReadOnly object containing the new size of the observed element when the callback is run. Note that this is better supported than ResizeObserverEntry.borderBoxSize or ResizeObserverEntry.contentBoxSize, but it is left over from an earlier implementation of the Resize Observer API, is still included in the spec for web compat reasons, and may be deprecated in future versions.


var contentRect = resizeObserverEntry.contentRect;


A DOMRectReadOnly object containing the new size of the element indicated by the target property.

If the target is an HTML Element, the returned contentRect is the element's content box. If the target is an SVGElement, the returned contentRect is the SVG's bounding box.


The following snippet is taken from the resize-observer-text.html (see source) example. This uses a simple feature detection test to see if the browser supports the newer ResizeObserverEntry.contentBoxSize property — if so, it uses that to get the sizing data it needs. If not, it uses contentRect.

const resizeObserver = new ResizeObserver(entries => {
  for (let entry of entries) {
    if(entry.contentBoxSize) { = Math.max(1.5, entry.contentBoxSize.inlineSize/200) + 'rem'; = Math.max(1, entry.contentBoxSize.inlineSize/600) + 'rem';
    } else { = Math.max(1.5, entry.contentRect.width/200) + 'rem'; = Math.max(1, entry.contentRect.width/600) + 'rem';



Specification Status Comment
Resize Observer
The definition of 'contentRect' in that specification.
Editor's Draft Initial definition.

Browser compatibility

Update compatibility data on GitHub
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidFirefox for AndroidOpera for AndroidSafari on iOSSamsung Internet
contentRectChrome Full support 64Edge Full support 79Firefox Full support 69IE No support NoOpera Full support YesSafari No support NoWebView Android Full support 64Chrome Android Full support 64Firefox Android No support NoOpera Android Full support YesSafari iOS No support NoSamsung Internet Android Full support 9.0


Full support  
Full support
No support  
No support