title: Leaflet map width in metres
body: <p>I want to have a button that creates a circle on my leaflet map. 
  The circle should be placed in the map Center and the diameter should be 75% of the current  displayed area width.
  To get the <code>lat</code> and <code>lgn</code> of the Center was easy. But I don't know how the 75% of the map with in <strong>metres</strong> for the radius. </p>
  
  <p>I tried the Method <code>getsize</code> but it returns the width in <strong>px</strong>. But I need this in <strong>metres</strong>.
  Is there a plugin? Or is it possible to calculate it with the zoomlevel and the Pixel from getsize?</p>