title: When I convert from px to rem units how should I decide how many rems to give the width of an <input>
body: <p>I have the following:</p>
  
  <pre><code>&lt;input maxlength="4" style="width: 50px;" type="text" data-ng-model="pidUpper" /&gt;
  </code></pre>
  
  <p>I would like my input box to hold a maximum of 4 characters. Is there some formula that I should use when deciding on the width if I am using rem units?</p>