Use a dress tape measure and place the beginning under your breasts at the centre of your breastbone. From there, wrap the rest of the tape around your chest until it meets the start of the tape. Mark on the tape where it met and jot down the measurement in inches, which should be above 24 inches.
Now you need to round the previous number up to the nearest whole number. If it lands on an odd number, you need to go up to the nearest even number. This final number is your band size.
The next step is to measure the fullest part of your breast, roughly nipple level. Hold the start of the tape in the centre and wrap the rest around you until they meet. Mark the tape and once again round up to the number to the nearest whole number and jot it down.
Cup size is not measured in the inches, but instead you need to work out the difference between your under-bust and your over-bust measurements. You can use a chart, which is for UK sizes, to find out your cup size based on what the difference between your measurements is.
Take the band measurement and the cup size and you have your bra size.