How to Measure Yourself at Home 

Band Size 

 

You should be wearing an unlined, non-padded bra. Do not measure over your clothes!
Run the measuring tape all the way around yourself where your band sits, being careful that the tape measure is level. It should be as snug as possible without digging . 
If you do not get a whole number (31.5 inches) round up to the nearest whole number (32 Inches). Now use the band size chart below to work out your size. 34 Inches does not mean your band size is 34. 

Cup Size 

 

Run the measuring tape around your back, just under your shoulder blades and up around the fullest part of your bust. The tape measure should just skim the unlined and non-padded bra you are wearing. 
Subtract your band size (explained above) from your bust measurement. The difference in inches corresponds to your cup size. For instance, if your bust measurement is 39 inches and your band size (once worked out in accordance with the size chart below) is 36, the difference will be 3, this is equal to a C cup, meaning your bra size is 34C.