My lovely husband George shall demonstrate.
don't ask questions
Women have a strange aversion to knowing what their measurements are, they tend to prefer generic sizes instead. Women, empower yourselves! Knowing what that measuring tape says can be a tool for good! If you buy yourself an inexpensive measuring tape and keep it in your purse, suddenly guessing if something will fit you is...well..less of a guess. Is there a blouse you like but don't have time to try it on? If you know your bust measurement is 40", measure the blouse on the hanger at the bust from side to side, pulling so it's taught. Take that measurement and double it, and that's its size all the way around. Did it measure 20" from side to side? Than your 40" bust should fit. When inquiring over the phone if a store has a certain size, give the clerk your waist measurement instead of a number, and she'll be able to give you a more accurate answer. Shopping for a child? How often have you had to tell a clerk, "Well, she's twelve, but she's tall for her age so a child's size twelve might be too short, so she might be more like a small adult, but then it might be too big so maybe she's a size 1?" If you have one little measurement, it's a whole world easier.
Little tricks like that only work if you've measured yourself properly. You may consider your waist to be the area a couple of inches below your belly button, but makers of clothing consider the waist to be the point at which your body creases when you bend to the side, which is usually above your belly button. The chart below is typical of what seamstresses use when building clothing. Note on the figure whose back is facing us where they mark the waist to be. The slight V just below the number five is where most people think their waist is.
If you shop online it's vital to know what your measurements are, as most stores have a sizing chart like this one from MyBabyJo.com . You'll notice an interesting thing as you observe the size charts of different shops: The more upscale the store, the larger your generic size will usually be. That's because places like Walmart like to do what's called vanity sizing. As time has passed people have tended to get bigger, but we still want to feel like we're small. So a size ten today is not the size ten of yesteryear.
In example, based on Walmart's website, a woman with a 32 1/2" bust would be a size 2.
Note what size a woman is with an even smaller bustline, based off of this old 1940s dress pattern.
Of course dress patterns are a little differently sized than store bought clothing, but the point still stands.
I suggest printing off one of the charts above and taking a moment to figure out what your measurements really are. Using the chart as a guide to where your measuring tape should go for each body part you're measuring, be sure the tape wraps around you snugly but not too tight (or too loose), and is parallel to the ground. Wear clothing that isn't baggy. For women, be aware that your bust measurements can change depending on the bra you're wearing, so if you're measuring yourself to find a formal dress, wear the bra you'd wear with the dress. If you're concerned you're just not measuring yourself correctly, drop by your local costume shop or tailor and someone will gladly help you out. Don't be afraid of what the numbers might show you. Knowing your actual size, knowing your true measurements, will not only save you some unnecessary frustration but may also help you find clothes that actually fit. And as they say, "Knowing is half the battle."