Women's sizing can be tricky when it comes to jeans. Are you a 2, 8 or a 10? If you're shopping for designer denim you've got to know if you're a 29, 30 or 31. What's the connection? It's not difficult to figure out once you size yourself for denim and hit up a standard conversion chart. After you've put it together, you'll be shopping like a pro and will stop wasting your time in the dressing room squeezing into sizes that aren't right for you.
Wrap the measuring tape around the smallest part of your waist. No cheating! Resist the urge to make it snug for a smaller waist size. Keep the tape comfortably close to your skin without pinching and record the number on the tape that meets with "0" on its opposite end. Write the number down.
Wrap the tape around the widest part of your hips. Write the number down.
Peep a standard conversion chart. These are available on any retailer's website under the link "size" chart. You can also find universal size charts online and even see what your size is in Europe and Japan, just in case you're a baller who does her shopping internationally.
Look up your size in inches on the chart and look at what single-digit size it corresponds to. For example, if you've got a waist between 27 and 28 inches with hips between 38 and 39 inches, you're in the medium (8 or 10) range. Stick to those sizes at the store and go up or down according to how they feel and fit.
When in doubt you should size down in jeans. Denim stretches and you'll wash them less often if you squeeze in and then wear them around, letting them conform to your body. If you buy a size up and they're a little loose to begin with, you'll be swimming in them at the end of the day.