We all know the Godzilla gets bigger every time he turns up so assuming that this growth is exponential and will not stop or slow down (because thats more fun) you end up with this graph.

The formula is this
EXP(0.013209094*year) * 0.00000000107165749235131

By the end of the century Godzilla has comfortable topped 1000ft
and finally pases a mile by 2213 and reaches its second in 2266
10 miles in 2387
in the early 2900s Godzilla out grows the earth, which is convenient as all the people fleeing from the earth he destroyed need somewhere to stay
A light year is pasted in 4439
5308 the galaxy is outgrown
6351 Godzilla fills the observable universe
Beyond that only Godzilla will know, but not yet

You can also copy the formula into a spread sheet to work out however big Godzilla was before he became a movie star. For example if the trend hold back in time (which it should because its cute) then he was 16ft tall at the start of the American revolution (any Americans that haven't imagined that Godzilla and Washington teaming up have probably been bitten by a were-Canadian) whilst in 1700 Godzilla was 6 feet tall and presumably fought alongside Jack Churchill (yes they are related)