See Cardplayer52s reply.
Many people simply quote numbers of bb without any reference to a context.
The crucial difference when it comes to stack sizes is how many bets / raises you can make before you get allin because this affects the implied odds you offer or get.
For example, if you can get more than 10% of your stack in preflop, you are denying any villain a chance to make ev by set-mining.
However, if you are 500bb deep and you 2b utg to 55bb, are you going to be called by any sensible player or will everyone except AA, KK (mayhe) and AK poss fold? If, though, you rsise to 3bb and get called, you have one pair with 497bb left , three more streets of betting and 6-7bb in the pot. Betting and raising blindly in this context is not going to end well v a decent player.
Dan Harrington's Cash books have a page where the exact number of 1/3, 1/2, 2/3, 3/4 and pot bets that can be made with varying stack sizes.