collections.js

// `mongo 127.0.0.1/MMApp collections.js`

function size(size) {
  var unit, res, factor=1;
  ['B', 'KB', 'MB', 'GB', 'TB'].every(function(unit_) {
    factor_ = factor*1024;
    res = size/factor_;
    unit = unit_;
    if(isNaN(res) || res < 1) {
      return false;
    }
    factor = factor_;
    return true;
  });
  return [Math.sigFig(size/factor, 3), unit].join(' ');
}

var totalSize = 0,
  totalDisk = 0;
db.getCollectionNames()
  .forEach(function(collection){
    var stats = db[collection].stats();
    totalSize += stats.size;
    totalDisk += stats.storageSize;
    print('Name:', collection);
    print('Records:', stats.count);
    print('Size:', size(stats.size));
    print('Disk:', size(stats.storageSize));
  })

print('\nTotals:')
print('Size:', size(totalSize));
print('Disk:', size(totalDisk));