How to Accurately Determine the Dimensions of HTML Elements?

Determining the Actual Dimensions of HTML Elements

When attempting to align an HTML element within the browser's viewport, it is essential to accurately obtain its actual width and height. This requires leveraging specific properties and functions supported by various browsers.

.offsetWidth and .offsetHeight

For determining the width and height of an element without considering CSS transforms, use the .offsetWidth and .offsetHeight properties. These properties are directly accessible on the element, unlike .style.

var width = document.getElementById('foo').offsetWidth;

getBoundingClientRect()

The .getBoundingClientRect() function provides a more precise readout of an element's dimensions and location after CSS transforms have been applied. It returns floating-point numbers indicating the following attributes:

console.log(document.getElementById('foo').getBoundingClientRect())
DOMRect {
    bottom: 177,
    height: 54.7,
    left: 278.5,​
    right: 909.5,
    top: 122.3,
    width: 631,
    x: 278.5,
    y: 122.3,
}

Browser Support

Property/Function	Browser Support
.offsetWidth/.offsetHeight	All major browsers
getBoundingClientRect()	All major browsers except Internet Explorer 8 and below

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