index.js

var tb = require('tilebelt')
var turf = require('turf')

var columns = ['Zoom', 'Tile size at equator (km)', 'Resolution at equator (m)']
console.log(columns.join('|'))
console.log(columns.map((c) => c.replace(/./g, '-')).join('|'))
for (var z = 0; z < 22; z++) {
  var tile = tb.tileToGeoJSON(tb.pointToTile(0, 0, z));
  var area = turf.area(tile);
  console.log([
    z,
    format(Math.sqrt(area) / 1000),
    format(Math.sqrt((area / (256 * 256))))
  ].join('|'))
}

function format (num) {
  return num < 2 ? num.toFixed(2) : Math.round(num)
}