Finding your bra size isn't hard - it just requires a measuring tape and a little simple math.
Note: There are (kind of goofy) illustrations of boobs in the following steps; if they offend you, I'm sorry in advance. If it offends you that they're just drawings (and not real boobs), sorry about that too.
Step 1: Measuring the Band Size
Round all fractional measurements to the nearest whole number. If the number you get is even, add 4 inches; if it's odd, add 5 inches - jot that number down, it's your band size (the 34 portion of 34D, etc.)
When measuring, it may help to have someone else measure you to ensure that the tape is not twisted, and that it's parallel to the floor around the back.
Step 2: Measuring the Cup Size
Round all fractional measurements to the nearest whole number.
From this number, subtract the number for the band size - this will tell you your cup size (see chart in next step).
Step 3: Getting a Better Bra
A few things to remember:
1. The center portion of a bra should fit between the breasts and should sit against the skin, not gap outwards.
2. Straps should not dig into the shoulders or hurt. If they do, try loosening them slightly, or try adjusting the band of your bra to make it looser.
3. The back band of the bra should sit across your back below the shoulder blades. If it pulls upwards, try loosening the shoulder straps.
4. If your bra has underwire, they should not dig in to your body or feel uncomfortable or painful - this is a sign that the bra does not fit you well.
5. The fabric of the cup portion should not bunch up (it's too big) or not cover the breast (too small).
6. If you gain or lose a lot of weight, you should re-measure and consider getting new bras as ill-fitting ones are rather uncomfortable.