title: What is difference between CSS em and ch units?
body: <p>What is difference between CSS <em>em</em> and <em>ch</em> units?</p>
  <p>I have been using <em>ch</em> in my stylesheet, but <em>em</em> seems more common. What is the difference between them?</p>
  <p>I understand that 20ch would give enough space for 20 zeroes. I don’t understand what em is. Does it give enough space for 20 M's or is it 20 x fontsize, i.e. size 16 font would give 320, but 320 of what unit? I don't get if they are almost the same or completely different.</p>