not all grow at the same rate, but if you buy a 1/2 redcrab you can be fairly sure that in just over 12 months you have a crab of 1 and 1/2 to 2 inches. at this point the number of moults will decrease to, roughly, one every twelve months
Thanks for the feedback ! Both my new crab and the original crab have molted in the last few days, so i'm much happier that the tank setup and food etc is ok... Fingers crossed.