As a former AVID bicyclist for around 25 years, I can tell you that "Bob A" is partially correct. It's the inseam measurement that you need to consider when buying a bicycle, but it's often spoken in terms of inches, as you ask. Please let me advise you on buying a bicycle since I have so much experience buying and riding them.
I don't know what your budget is, but, for ya'll's sake, do NOT buy one from WalMart, KMart, Target and the likes. Go to a REAL bicycle shop and get measured for an exact fit / height of a bicycle, and buy one that isn't one of those "two-wheeled-tanks" as I call bikes bought at stores of the likes of those I've named. It will make a HUGE difference in how much you ride your bikes, and how happy you are with them, and, many bicycle shops have their own riding clubs which are full of very fun people at all stages of bicycling experience, and they can be a LOT of fun, as was my experience with the club I belonged to in Athens, Texas. The rides are leisurely, and we often met for club meetings, followed up by a club "eat-out" at our favorite pizza parlor, and at times we'd put together one of those events where everyone brings a dish of their favorite food over to one of the club members' house, and we'd have more fun just sitting around talking and bragging, and eating, etc., after a fun ride. And if you really get into bicycling, you can eat all the food you want because bicycling will burn calories galore, and keep you trim and fit as well. Now, you and your boyfriend may not have had such social experiences with your bicycling in mind, but, I HAVE to say that you need to go to a REAL bicycle shop and get properly fitted for a good bike so you'll really enjoy bicycling. I've ridden tens of thousands of miles over the years, in going to and from work and school, and in leisurely riding alone and in group / club rides and in massive rides that drew thousands of participants, and in races. I hope whatever your need is, someone fits you right for a bicycle, and it won't happen at WalMart, Target, KMart, or the likes. You'll love a good , REAL, bicycle shop. God Bless you both.
