Calculate text width with JavaScript

In HTML 5, you can just use the Canvas.measureText method (further explanation here).

Try this fiddle:

  * Uses canvas.measureText to compute and return the width of the given text of given font in pixels.
  * @param {String} text The text to be rendered.
  * @param {String} font The css font descriptor that text is to be rendered with (e.g. "bold 14px verdana").
  * @see
function getTextWidth(text, font) {
  // re-use canvas object for better performance
  const canvas = getTextWidth.canvas || (getTextWidth.canvas = document.createElement("canvas"));
  const context = canvas.getContext("2d");
  context.font = font;
  const metrics = context.measureText(text);
  return metrics.width;

function getCssStyle(element, prop) {
    return window.getComputedStyle(element, null).getPropertyValue(prop);

function getCanvasFontSize(el = document.body) {
  const fontWeight = getCssStyle(el, 'font-weight') || 'normal';
  const fontSize = getCssStyle(el, 'font-size') || '16px';
  const fontFamily = getCssStyle(el, 'font-family') || 'Times New Roman';
  return `${fontWeight} ${fontSize} ${fontFamily}`;

console.log(getTextWidth("hello there!", "bold 12pt arial"));  // close to 86

If you want to use the font-size of some specific element myEl, you can make use of the getCanvasFontSize utility function:

const fontSize = getTextWidth(text, getCanvasFontSize(myEl));
// do something with fontSize here...

Explanation: The getCanvasFontSize function takes some element’s (by default: the body‘s) font and converts it into a format compatible with the Context.font property. Of course any element must first be added to the DOM before usage, else it gives you bogus values.

el.remove()); // hackfix: don’t do this!
return el;

“hello there!”,

“hello there!”,
“` –>

More Notes

There are several advantages to this approach, including:

  • More concise and safer than the other (DOM-based) methods because it does not change global state, such as your DOM.
  • Further customization is possible by modifying more canvas text properties, such as textAlign and textBaseline.

NOTE: When you add the text to your DOM, remember to also take account of padding, margin and border.

NOTE 2: On some browsers, this method yields sub-pixel accuracy (result is a floating point number), on others it does not (result is only an int). You might want to run Math.floor (or Math.ceil) on the result, to avoid inconsistencies. Since the DOM-based method is never sub-pixel accurate, this method has even higher precision than the other methods here.

According to this jsperf (thanks to the contributors in comments), the Canvas method and the DOM-based method are about equally fast, if caching is added to the DOM-based method and you are not using Firefox. In Firefox, for some reason, this Canvas method is much much faster than the DOM-based method (as of September 2014).


This fiddle compares this Canvas method to a variation of Bob Monteverde’s DOM-based method, so you can analyze and compare accuracy of the results.

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