Anyone know the formula to calculate BB/100 for NLHE? For LHE, BB = Big Bet, so for NLHE does BB = the Big Blind or the Big Blind x2?

Up until the past few sessions, I've solely measured my success by the increase/decrease in bankroll. I've been keeping a few records lately however, and am curious to know what my BB/100 is.

As you can guess, I don't use PT and I'm not a mathematician.