Get width in pixels from element with style set with %?

javascript

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byNikita Barsukov·Feb 8, 2025

To transform an element's width from percentages to pixels, tap into JavaScript's getComputedStyle for precision, including the padding and borders in the measurement:

let element = document.querySelector('.yourElementClass'); // Your element's "call sign"
let widthInPixels = window.getComputedStyle(element).width;

getComputedStyle provides the rendered style of the element. The width property’s value is the exact pixel width, regardless of whether the original CSS value was a percentage.

JavaScript properties for pixel calculation

Using `clientWidth`

clientWidth yields the width that includes padding but excludes borders and scrollbars. It's a direct and reliable measurement for inner width.

let clientWidth = element.clientWidth; // Width, pads its tummy but says no to makeup and stilettos (borders and scrollbars)!

Resorting to `offsetWidth`

offsetWidth calculates the width, factoring in the padding, borders, and scrollbar. An all-inclusive measurement.

let offsetWidth = element.offsetWidth; // All-inclusive vacation package with padding, borders, and scrollbars!

Watch out! If width is set in percentages, elem.style.width will return the same percentage and not an equivalent pixel value.

When jQuery comes to rescue

jQuery's .width() furnishes the computed width in pixels. Forget all the pitfalls of raw JavaScript.

let pixelWidth = $(element).width(); // jQuery, the pixel whisperer

Manual calculations in complex scenarios

For certain situations, manual computations are necessary. Margins are not part of offsetWidth. If you require the full width, it involves separately fetching margins from getComputedStyle and adding them to offsetWidth.

Remember, clientWidth and offsetWidth values could differ due to scrollbar width, so pick the one that suits your case (with or without the scrollbar look).

To set width using pixels explicitly, you can directly assign it like so:

element.style.width = '50px'; // When life gives you pixels, make width!

Navigating the complexity: Scrollbars and borders

Scrollbar Calculations

Some loves are complex; so is the love for scrollbars in width calculations:

clientWidth ignores the scrollbar width (keeping the relationship exclusively with inner width).
offsetWidth includes it, occasionally adding more drama to your layout calculations.

If scrollbar size is significant for your calculations, you might need to account for its width separately:

let scrollbarWidth = element.offsetWidth - element.clientWidth; // Scrollbar, the annoying third wheel between offsetWidth and clientWidth!

Evaluating borders

Borders can make width calculations more challenging. Remember, clientWidth excludes them, while offsetWidth includes them in its considerations.

When you want to accommodate border size absolutely, derive it using getComputedStyle:

let borderLeftWidth = parseFloat(getComputedStyle(element).borderLeftWidth); // The left-side bodyguard
let borderRightWidth = parseFloat(getComputedStyle(element).borderRightWidth); // The right-side escort
let totalWidthWithBorders = clientWidth + borderLeftWidth + borderRightWidth; // Width with its security detail