Believe it or not, at least 80% of women wear the wrong size bra. The most common mistake is wearing a band size which is too big, and/or a cup size which is too small. Although the average bra size is often quoted as 36C, most people who wear this size should actually be wearing either a 34D, 34DD, 32DD or 32E bra. The true average bra size is around 34DD. Cup sizes are in proportion to the band size, so a D cup, for example, is not the same size in every bra. A 32D is the same size as a 34C or 36B, but on a smaller frame. A 28F is actually 2 cup sizes smaller than a 38D. If you are fairly slim, then you may well need a large cup size even though your bust doesn’t look any bigger than average. You may not think of yourself as being busty, but in moving to a smaller band size you will find that you need a bigger cup size.
Your bra size changes as your weight fluctuates throughout the seasons and the years. Sometimes you go for so long wearing a specific size that you don’t realize it doesn’t fit well anymore and you stop noticing the discomfort. If you’re looking for a better fit, here’s how to find your true bra size.
Important note – the measurements used in the steps of this guide refer to standard UK bra sizing. Although US bras are theoretically sized according to the same system, there is considerable variation between brands, so if you are in the US you may find you need a bigger band size and/or a smaller cup size than that indicated here. For example, A 32E in one brand may be equivalent to a 34DD in another.
Wear your best supporting bra. The bra doesn’t have to fit perfectly. The objective is to get your breasts to the position that the ideal bra would support, with the weight suspended comfortably. This step is optional, however, so if you can’t find a bra with good support, continue with the measurements.
Measure your band size. Run a tape measure all the way around your body just underneath your breasts and take a measurement in inches. Make sure the tape measure is horizontal and fairly snug. Your arms should be down. Round to the nearest even number. This should be your band size. For instance, if you measured 31 inches, your band size should be 32. If you measured 34.5 inches, your band size should be 34. Many bra fitting guides and calculators will tell you to add four or five inches to your underbust measurement, but this is not correct. The old method was devised by Warners in the 1930s when bra design was in its infancy and does not work with modern, elasticated bras.
Measure your bust size. Measure loosely around the fullest part of your bust in inches (not too tightly or the tape measure will squash your breasts down.) If you don’t have a bra, or if the one you have is very poorly fitting, bend over so your back is parallel to the floor and measure around your chest, over your nipples. Round this measurement up to the nearest whole number.
Calculate your cup size. Subtract the band size from the bust measurement and determine your cup size as follows: (This calculation may be less accurate for larger cup sizes.) If your underbust measurement was an odd number and you had to round it up, you may find it more accurate to use your raw underbust measurement rather than your band size.
Less than 1 inch = AA cup
1 inch = A cup
2 inches = B cup
3 inches = C cup
4 inches = D cup
5 inches = DD cup
6 inches = E cup (US DDD)
7 inches = F cup (US DDDD)
8 inches = FF cup
9 inches = G cup
Try on a bra with the band and cup size you’ve arrived at in these steps. You should not regard this as your definitive size until you have tried on a few bras, and even then you will often find you need a different size in different brands or styles of bra. It is not possible to calculate the exact volume of the breasts using only two measurements, so this should be taken as a guide only.
Check the band size. The correct band size is the smallest you can comfortably wear. It needs to be tight enough that the bra is still fairly supportive without weighing down heavily on the shoulder straps.
You should be able to run your fingers around the inside of the band, but not much more. A good rule of thumb is that you should be able to fit no more than a fist under the back of the bra.
It should fit on the biggest adjustment, but will probably be too tight if you try to fasten it on the smallest size. Bras are designed to fit like this so that you can tighten the band as the elastic starts to wear out.
If the band is roomy enough for you to be able to comfortably fasten it on the tightest adjustment, try a smaller band, for example if a 32D is too loose, try a 30DD. Note that the cup size has to be changed when you move to a different band size – for every band you go down, you must go up by one cup size in order for the cups to remain the same capacity.
If you can only just fasten the bra and the band is painfully tight, even on the biggest adjustment, then go up a band size, for example if a 32D is too tight, try a 34C.
Check the cup size. The correct cup size is the biggest you can completely fill out with no wrinkling of the fabric or space in the cups. You should fill out the cups, but not bulge out anywhere, even in low cut or pushup bras.
Check around the cups for any bulging, not only along the top edges but also at the sides under your arms.
Make sure the underwire encloses your whole breast and lies flat against your rib cage.
If the cups are too big, go down a cup size.
If they are too small, or even if they seem to fit ok, try on a bigger cup size as well to double check. It’s a lot easier to tell if they are too big than too small.