How to tell how far you are from weeks to months...

I have to say that whenever people ask me how far along I am it's so much easier to tell them in months.  As soon as I say "29 weeks", they say "and how many months is that?"  But it's just silly b/c going by weeks alone pregnancy is 10 months (40 weeks, 4 weeks in a month, 10 months!) so then the trimesters are all screwed up!  I think people just don't want to change the system that has been around for so long.  No matter how you choose to say it, you're in the second "trimester"  lol!  Good Luck