Wikipedia: https://en.wikipedia.org/wiki/Geohash
JS interactive: http://www.movable-type.co.uk/scripts/geohash.html
Length Cell width x Cell height
1 ≤ 5,000km × 5,000km
2 ≤ 1,250km × 625km
3 ≤ 156km × 156km
4 ≤ 39.1km × 19.5km
5 ≤ 4.89km × 4.89km
6 ≤ 1.22km × 0.61km
7 ≤ 153m × 153m
8 ≤ 38.2m × 19.1m
9 ≤ 4.77m × 4.77m
10 ≤ 1.19m × 0.596m
11 ≤ 149mm × 149mm
12 ≤ 37.2mm × 18.6mm