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Editorial Team
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Asked: 2026-05-27T01:35:28+00:00

When using a fixed width font , I’d like to specify the width of

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When using a fixed width font, I’d like to specify the width of an HTML element in characters.

The “em” unit is supposed to be the width of the M character, so I should be able to use it to specify a width. This is an example:

<html>
  <head>
    <style>
      div {
        font-family: Courier;
        width: 10em;
      }
    </style>
  </head>
  <body>
    <div>
      1 3 5 7 9 1 3 5 7 9 1
    </div>
  </body>
</html>

The result is not what I wanted as the browser line breaks after column 15, not 10:

1 3 5 7 9 1 3 5
7 9 1

(Result in Firefox and Chromium, both in Ubuntu.)

Wikipedia’s article says that an “em” is not always the width of an M, so it definitely looks like the “em” unit can’t be trusted for this.

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1 Answer

  1. Editorial Team

    1em is the height of an M, rather than the width. Same holds for ex, which is the height of an x. More generally speaking, these are the heights of uppercase and lowercase letters.

    Width is a totally different issue….

    Change your example above to 

    <div>
    <span>1</span> 3 5 7 9 1 3 5 7 9 1
</div>

    and you will notice width and height of the span are different. For a font-size of 20px on Chrome the span is 12×22 px, where 20px is the height of the font, and 2px are for line height.

    Now since em and ex are of no use here, a possible strategy for a CSS-only solution would be to

    1. Create an element containing just a &nbsp;
    2. Let it autosize itself
    3. Place your div within and
    4. Make it 10 times as large as the surrounding element.

    I however did not manage to code this up. I also doubt it really is possible.

    The same logic could however be implemented in Javascript. I’m using ubiquitous jQuery here:

    <html>
  <head>
    <style>
      body { font-size: 20px; font-family: Monospace; }
    </style>
    <script 
      type="text/javascript" 
      src ="https://ajax.googleapis.com/ajax/libs/jquery/1.7.0/jquery.min.js">
    </script>
  </head>
  <body>
    <div>1 3 5 7 9 1 3 5 7 9 1</div>
    <script>
      $('body').append('<div id="testwidth"><span>&nbsp;</span></div>');
      var w = $('#testwidth span').width();
      $('#testwidth').remove();
      $('div').css('width', (w * 10 + 1) + 'px');       
    </script>
  </body>
</html>

    The +1 in (w * 10 + 1) is to handle rounding problems.

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