Google Maps Tile Scales
mattwigway
I found this buried deep in an appendix of the Mapnik XML Schema Reference, and I thought it so useful I am reposting it here:
Zoom level Scale denominator
0
559,082,264
1
279,541,132
2
139,770,566
3
69,885,283
4
34,942,642
5
17,471,321
6
8,735,660
7
4,367,830
8
2,183,915
9
1,091,958
10
545,979
11
272,989
12
136,495
13
68,247
14
34,124
15
17,062
16
8,531
17
4,265
18
2,133
19
1,066
20
533
These are used not only by Google Maps, but also by Bing Maps, OSM, CloudMade and many others, and in fact just about any Google Mercator tile source.