To calculate your bra size, all you need are two measurements. Your underbust measurement is the band size and will be the number on your bra size. The 2nd measurement is your overbust measurement and corresponds to the letter on your bra size.
Start by finding a soft measuring tape and make sure you're not wearing any outer garments as this can affect the measurement.
To find your band size, wrap a soft measuring tape under the bust, right up against the ribcage. Using this number you can find the corresponding underbust row.
Next, take your tape measure and go around the fullest part of your bust. Look in the mirror to make sure the tape is straight. Use this number to find your cup size within the column of your corresponding band size.
As bra sizes are not universal, use our BRANDS GUIDE to find your size in each brand. The chart below is one example of a brand's sizing guide.