title: How is font size calculated?
body: <p>I have a complex js function with an equation in which I actually need to understand how much space in pixels font sizes take up.</p>
  
  <p>I have noticed that some font's sizes are different depending on the font.</p>
  
  <p>How is a font's size calculated? If its set to <code>12px</code>, in css, what does the <code>12px</code> mean? Is that <code>12px</code> wide? High? Or is it a diagonal pixel measurement?</p>