How to measure bra size
To measure bra size, take your underbust below your bust, then measure around the fullest part of your bust with the tape level and snug.
Where the tape goes
Bust
loose, level, at the fullest point
Underbust
snug, level
How to measure, step by step
- Stand upright with relaxed shoulders and use a soft tape measure.
- Underbust: wrap the tape around your ribcage directly under your bust. Keep it level and snug, not tight, and note the figure.
- Bust: wrap the tape around the fullest part of your bust. Keep it level and loose, not pressing, and note the figure.
- Write both figures in the same unit, inches or cm, then enter them in the calculator or use one of the three rules below.
Three published rules
Published sources do not agree on one rule. Here is each rule applied to the same example: an underbust of 30 in and a bust of 36 in.
Underbust method
Round your snug underbust to the nearest even number of inches. That is your band, and an exact odd number rounds up. Your cup is your bust minus the band, rounded to a whole inch.
Example: band 30, difference 6 in, cup DDD/F, so US 30DDD/F.
Add-4 method
An older rule, still on some charts: round your underbust to a whole inch, then add 4 if that number is even and 5 if it is odd. The cup is your bust minus that band.
Example: band 34, difference 2 in, cup B, so US 34B.
EU method
Round your underbust in cm to the nearest multiple of 5. That is the EU band. The cup letter comes from your bust in cm minus that band, in steps of 2 cm. FR/BE bands are higher numbers for the same label.
Example: EU band 75, difference 16.44 cm, cup C, so EU 75C and FR/BE 90C.
Try your own numbers
Enter your underbust and bust to see all three rules side by side.
Place the tape around your body under your bust to measure the underbust, and hold it snug. Keep the tape level all the way around. For the bust measure, wrap it around the fullest part of your bust. Keep it snug without pulling it tight.
The underbust method rounds the underbust to the nearest even number of inches for the band. An exact odd whole number goes up. The difference is the bust minus the band, rounded to whole inches, and it determines the cup. An underbust of 30.9 in gives band 30, while exactly 31 in gives band 32. The add-4 method rounds the underbust to the nearest whole inch, then adds 4 to an even number or 5 to an odd number. The EU method rounds the underbust in centimetres to the nearest 5 cm. Its cup letter follows the difference in centimetres, starting with AA at 10 cm and moving up one letter every 2 cm to H, up to 28 cm. On a boundary, the higher letter applies.
For the worked example, the underbust is 30 in (76.2 cm) and the bust is 36 in (91.4 cm). The underbust method gives band 30 and a difference of 6 in: US 30DDD/F, UK 30E, EU 65F, FR/BE 80F, AU/NZ 8E, and JP 65G. The add-4 method gives band 34 and a difference of 2 in: US 34B, UK 34B, EU 75B, FR/BE 90B, AU/NZ 12B, and JP 75C. The EU method gives EU band 75 and a difference of 16.4 cm: EU 75C and FR/BE 90C. The EU method gives EU and FR/BE sizes only.
The methods disagree because they apply different band and cup rules. Published charts also differ in rounding: one rounds the bust up, another rounds the band to the nearest even number, and a third uses half-inch ranges. A calculated size is a starting point; methods and charts differ, and JP letters vary by brand. Measure again and try on.