Can I measure my bottom bracket size without removing the cranks?
As, if not more important than length, is the chain line.  Obviously related, but enough variation to cause problems, as I found out not when I got into my own bike maintenance. Sheldon (as always) shows a way to measure chain line here. The same page has  table of various Bottom brackets and the length and chain-line measurements. 

Essentially you measure from the center of the chain rings (triple is easy, double measure half way between the rings) to the center of the seat tube to get your chain line. Then you should be able to match up a BB that will suit.