Are my boobs bigger than my friends?

I just went to la senza and got measured as a 30F and my friend who went there got measured as a 32DD, but when i told her she went of in a hissy fit saying that mine aren't bigger than hers and i must be lying. I didn't believe that i really was a 30F though because la senza sizes are really weird so i went to marks and spencers and the measured me as a 32C and when i told her she got all smug, but if i was bigger than her in that shop, shouldn't i be bigger than her anywhere else? My other friend told me though that the friend with 32DD's, when she buys bras from any where except la senza the 32DD's are way too big. I'm really confused about sizing now :L