code: function(ll, map) {
      var pointC = map.latLngToContainerPoint(ll); // convert to containerpoint (pixels)
      var pointX = [pointC.x + 1, pointC.y]; // add one pixel to x
  
      // convert containerpoints to latlng's
      var latLngC = map.containerPointToLatLng(pointC);
      var latLngX = map.containerPointToLatLng(pointX);
  
      var distanceX = latLngC.distanceTo(latLngX); // calculate distance between c and x (latitude)
      return distanceX;
    }
docs: http://wiki.openstreetmap.org/wiki/Zoom_levels http://stackoverflow.com/questions/27545098/leaflet-calculating-meters-per-pixel-at-zoom-level