How to use the bra size calculator
- In "Find my size" enter your bust and underbust in cm to see the Korean, US, UK, EU, French/Spanish, Japanese and Australian labels at once.
- To translate a size you already know, open "Convert sizes" and pick the country, band and cup.
- The sister sizes under the result are alternatives to try on when the band or cup does not fit well.
How bra size is determined
A bra size has two parts, the band and the cup. The band is your underbust measurement rounded to a 5 cm step, and the cup comes from the difference between your bust and underbust. In the common Korean and Japanese system a difference of about 10 cm is an A cup, and each extra 2.5 cm moves up one letter to B, C, D, E. For example, an underbust of 70 cm with a bust of 85 cm gives a 15 cm difference, which is 70C.
Labels differ by country. The US uses even band numbers based on inches (30, 32, 34), while France and Spain add 15 to the Korean number (85, 90). From the E cup on, the US continues with DD and DDD and the UK with DD, E and F, so the same cup volume carries different letters. This calculator shows those differences from one conversion table.
Measuring accurately and shopping tips
Keep the tape level with the floor and check in a mirror that it does not sag at the back. Measure the bust standing upright without leaning forward. Breast size can change with the menstrual cycle, weight changes, pregnancy and nursing, so measure again when your situation changes.
The result is a starting point. In an underwired bra the whole breast should sit inside the cup and the wire should not press on breast tissue, and the band should be snug enough to fit only two fingers underneath. If the straps dig in because they carry most of the load, the band is probably too loose. Wireless, sports and seamless styles stretch differently, so going one size up or down is common.
Tips for buying from overseas
- Check which country the size chart on the shopping site uses.
- British brands continue cups as DD, E, F, FF, which differs from US labels.
- The same size can fit looser or tighter between brands, so read reviews.
- Check the return policy and whether lingerie can be returned.
- Buy one piece first from a new brand and add more after checking the fit.
FAQ
How do I measure bust and underbust?
Stand up in a thin bra or no bra and keep the tape level with the floor. Measure the underbust snugly but not tightly around your ribcage right below the breasts after breathing out, and measure the bust around the fullest part without pressing. Measure twice and use the average to reduce error.
Is a Korean 75B the same as a US size?
Band numbers correspond, with Korean 75 equal to US 34 and Korean 70 equal to US 32, and cups A to D use the same letters. From the E cup up, letter systems differ by country, so it becomes US DD and DDD. Even with the same label, brands can differ by about half a size.
When should I use sister sizes?
If the band is loose, the size with a band one step smaller and a cup one step larger keeps nearly the same cup volume. If the band is tight, go one band up and one cup down. Try them on and check that straps do not slip and wires do not press.
Notes & limitations
This calculator is a reference tool based on common conversion charts. Real fit differs between brands and products, so try on in a shop when possible. If you notice pain or a lump in the breast, that needs a medical professional, not a different bra size.