I talk a lot about bras and bra fittings so it's only appropriate to have a page about it.
Remember, this is only an approximation. The best way to get a well-fitting bra is to try them on. However, if you're like me and don't have anywhere locally where you can try on bras, then here's a good place to start.
1. Measure your underbust tightly. This is your band size. If you're in between (like me at 31") then you might be one lower or one above depending on the brand (so I would fluctuate between a 30 and 32 band). For a further discussion and exceptions to this rule see All about Band Sizes.
2. Getting your bust size. This is tricky. If you're wearing a very ill-fitting bra measuring with your bra on can give you a measurement that's WAY too small (cough, not that I know from lots of personal experience... ). So I'll give you three other ways to measure and it might be worth it to consider those three measurements when you start trying on bras. All these measurements are taken WITHOUT your bra on.
a. Bend over and measure around your bust (over your nipples). This is a bust measurement.
b. Bend over and measure around each breast separately (over the nipple). This would give you the difference between bust and underbust (so the number used to find your cup size). It's worth it to do this no matter what to know if one breast is larger than the other and if so by how much.
c. Lay on your back and measure around your bust (over your nipples). This is another bust measurement.
3. Take the difference between your bust and underbust measurements and that number will find you your cupsize in the chart below:
4. Before buying a bra check how they determine the cup size! US and UK sizings are different. In the UK you have a lot of double up letters like a J and then JJ whereas in the US you just go straight through the higher end of the alphabet. Before buying make sure you know what system is being used, always ask if you are unsure!
5. Check your stats in bratabase. If you're lucky you'll find someone with similar measurements to your own there and can compare bras. If not please put in your measurements so others like you can be helped!!
6. See also the Bra Band Project. Women in a lot of different sizes have submitted photos of themselves and it's a great comparison to gauge your size. Also, feel free to submit your own photo (can be clothed or in a bra).
6. Buy a few different bras around your size. Make sure where you're buying from has a good return policy (sometimes they'll pay for shipping). Just to give you a good idea what to check, let's say you measure as a 32H. Then try buying a 32GG/32H/32HH/34GG. Now if you've found the bra you're interested in the bratabase you might be able to take some of the guess work out by reading the reviews.
6. Once you get your bras check to make sure that they fit properly. See the pages below for fitting help:
Pictures of a Well-fitting Bra vs. Poorly Fitting bra
Signs of a Poor Fitting Bra
7 Tips to check if your bra fits
Bras and Boobs during Pregnancy
New Baby, New Boobs, New bras
Is your profession bra fitting give you the right bra size?
How do you support big busted teenagers?
What life can do to your boobs and bra.
Bra Fitting and Lingerie 101
Different Sizing Systems
7. See photos of women with well-fitting bras on so you get a good idea if your bra is on correctly and fits well:
What does it mean to wear D or DD cups?
G and GG cups do they always stand for get a reduction?
How to use balkonetkas catalogue?
What has a correct bra fitting given to me?
Sophie Jenner blog
8. Special considerations. ALL breasts are unique and because of that bra fitting depends on a women's age, weight loss/gain history, pregnancy history, breast firmness, breast size etc. I'd encourage you to check out my Table of Contents, specifically, the section on Sizing which covers various fit issues that women commonly run into.