How to Find Your Current Size
To determine your current size, let’s take some measurements. If your top is thin you can leave it on (but take off any thick layers). Measure yourself with your (unpadded) bra on. Stand straight, relaxed, with your arms down, breathing normally. If you can, measure yourself in front of a mirror, so you can make sure the measuring tape isn’t twisted and that it’s parallel to the floor all the way around. Now, take 3 measurements:

1) Take Your Chest Measurement - Around your chest, right under your arms. This as a snug measurement.

To illustrate, Jen is late in her third trimester, and we’re helping to fit her into a nursing bra (if you can, it’s often easier to have a friend measure you). Taking her chest measurement, we get 37 inches.

2) Take Your Rib Cage Measurement – Just below your breasts. If you have someone helping measure you, and you are wearing a bra that your breasts are sagging in even a little bit, take your straps and pull up so that your breasts are lifted to where you would like them to be, and then have your friend measure your rib cage. This is also a snug measurement.

For this second step, we take Jen’s rib cage measurement and get 38 inches.

3) Take Your Bust Measurement - Across the fullest part of your breasts. As with the previous measurement, if you are wearing a bra that doesn’t position your breasts exactly where you’d like them to be, then hold your bra straps up so your breasts are lifted to their ideal spot, and measure across the fullest part (usually across the nipples). This is a loose measurement.

Measuring Jen, we get a bust measurement of 42 inches.

Now, we’re ready to determine your current size:

1. Take the larger of your chest measurement and rib cage measurements. If you get an odd number, round up. This is your rib band size.
2. Subtract that rib band size from your bust measurement. Every inch is one cup size, so you can count up (1=A, 2=B, 3=C and so on) or use the chart below to find that difference to determine your cup size.

For Jen, we take the larger of her chest measurement (37) and rib cage measurement (38) to get a rib band size of 38. We then subtract that from her bust measurement (42) to get a difference of 4 inches. From the chart above, we know that is equal to a D cup. So, Jen measures to be a 38D.

Here are some other examples:

Now that we have a good idea about current size, let’s look at what stage of pregnancy or nursing you are in right now, and what you are buying the bra for to make sure it will work for your current and future needs. First, let’s talk breast changes over pregnancy and nursing.

What Happens
As you may already know, one of the earliest physical signs of pregnancy can be breast tenderness. At some point in your pregnancy (often but not always around the second month), breasts will start becoming larger as they prepare to nurse the new arrival. Some women experience this as a feeling of fullness rather than actual increase in size, and others are very aware of needing a larger cup size.

Some women will continue to increase in cup size over the course of their pregnancy, and others find they have an increase during their first trimester, and not again until close to the end of their pregnancy. As well, as your belly increases in size, your rib cage (band) measurement will also likely increase. Women who are petite or carrying high will often experience more increase in rib band than women who are taller or carrying low. Overall, in our experience, most women increase one or two cup sizes and one or two rib band sizes over the course of their pregnancy.

Then, for the first few days after giving birth, when you breastfeed, your baby receives colostrum. At around the third day, your milk will ‘come in’. At that point, you can experience an increase of one or two more cup sizes from your third trimester.

Typically after about 6 weeks to a few months of nursing, these fluctuations settle down. You will have established your breastfeeding relationship and routine, and will usually decrease a few cup sizes. As well, around this point, your rib band size will begin to go back to your pre-pregnancy size. This is the size you will likely stay until you finish breastfeeding. That is, at about your pre-pregnancy rib band size, and up one cup size.

Here are some examples to illustrate:

What Size to Buy
Now - let’s look at what size to buy if you are currently in your third trimester, and are purchasing a bra to nurse your baby in. Again, remember each of us is unique so there is a chance this recommendation won’t work for you, but on average, we find it to be a great guide. We’ve used Bravado nursing bras as an example:

* Consider purchasing both of these sizes, as they will each work for you at different times. For example, you may prefer the full-front style of the Double Plus (++) for sleeping, or to give you more room in the cups when you’re feeling particularly full; in addition to the Plus (+) for daytime or when baby is feeding more frequently.