I have a question, how long is it for each zoom level?

It looks like each zoom level doubles the distance it has.

I measure it as follows, is it correct?
Zoom nm
10 ~= 83.2
11 ~= 41.6
12 ~= 20.8
13 ~= 10.4
14 ~= 5.2
15 ~= 2.6

Thanks
Li