How to measure your breasts
Using a tape measure, measure just under your breasts. Go without your bra for a more accurate fit. Make sure the tape measure is level and pull so it is snug. Write down the measurement in inches. This is your band size. If the number is odd, try bras in the sizes above and below, eg, if you measure 33, try a 32 and 34. Next, measure loosely the fullest part of your breasts (across the nipples), making sure the tape measure is level. Write down the measurement and then subtract the band size from this number. The difference in the numbers is your cup size. Refer to the chart below to get your bra size. The band measurement is across the top and the cup measurement is to the left hand side. If your band measurement is an odd number (eg 33) and the difference is 5, you could try a 32DD or 34DD as a starting point.
All bras have a “sister size”. This means that each bra size has a related size which holds the same volume. Cup size is relative only to the band size. If you want to sister size down, the band decreases a size and the cup increases. So a 36C becomes 34D. If you want to sister size up, a 36C would become 38B. The fit is generally not quite as perfect, but can be a good option if you are struggling to get the right size.
Just because your bra size might be X, doesn’t guarantee that this size will necessarily be the best fit in every style and manufacturer. Be prepared to occasionally move up or down a band or cup size and read more information about the right fit.