Bra Cup Size Guide

Use a piece of string and measure it against a ruler. Even rough measurements will point you in the right direction. While a professional bra fitting is ideal, our calculator gives you an accurate starting point. This cup size guide also has a bra fit guide that can help you identify signs you are wearing the wrong bra size.

Yes, up to DD they are identical in both sizing systems. After DD, the two systems diverge: US sizing goes DD → DDD/F → G, while UK sizing goes DD → E → F → FF. This split causes most of the confusion when shopping internationally. Use our size converter to translate between US, UK, EU, and AU systems instantly.

Sister sizes are bra alternatives that share the same cup volume on a different band. For example, 34C, 32D, and 36B all hold the same cup capacity -- the difference is how tight the band fits. This is useful when your size is sold out or a brand runs tight. Learn more in our sister sizes guide.

In the US, 34DD is the most commonly purchased size. But fitting experts estimate up to 80% of women wear the wrong bra size -- usually a band too large and cup too small. Use our bra size calculator to check your actual measurements.

Every 6 to 12 months, or after any significant body change such as weight gain or loss, pregnancy, breastfeeding, hormonal shifts, or starting a new exercise routine. Breast tissue composition and ribcage circumference both fluctuate over time, and even a half-inch change in either measurement can shift your bra size by one cup or band.

In US sizing, the sequence after DDD is G → H → I → J → K. DDD is also labeled F by many brands. There is no standalone E cup in the US system. UK sizing follows a different pattern: E, F, FF, G, GG, H, HH, JJ. Our breast size chart maps every cup letter across both systems side by side.

A D cup means there is a 4-inch difference between your bust and underbust measurements. As shown in our cup size guide, it is considered medium-large in US and UK sizing and corresponds to an EU D cup. At band 34, a D cup holds approximately 360 ml of volume.

In US sizing, DDD and F are the same size, both representing a 6-inch bust-to-underbust difference. Many US brands use the labels interchangeably. UK sizing uses E for this same measurement, not F. This is one of the most confusing crossover points between sizing systems, which is why a size converter is helpful when shopping across brands.

The band should sit level and snug around your ribcage. You should be able to slide two fingers underneath but no more. Signs like cup spillage, band riding up, and straps digging in all indicate a sizing issue. If the band rides up in the back, it is too loose — try going down one band size and up one cup size.

Yes. Hormonal fluctuations, aging, muscle development, pregnancy, and changes in body composition can all shift your bra size. Your bra measurement can change even without weight gain, which is why fitting experts recommend remeasuring every 6 to 12 months.

Falling straps usually indicate a band that is too large. When the band rides up, it pulls the straps to the outer edge of your shoulders. If your bra strap keeps sliding, a sister size with a tighter band often solves the problem. Try a sister size — one band size down, one cup size up.

One inch of bust-to-underbust difference. A D cup has a 4-inch difference while DD has 5 inches. Despite the double letter, DD is simply the next incremental size up from D, not double the volume. At band 34, a D cup holds approximately 360 ml while a DD holds about 450 ml -- a proportional increase, not a doubling.

Yes. EU sizing uses centimeters, adds 10 to 15 to band numbers, and uses sequential letters without doubles — no DD or DDD. A US 34D equals an EU 75D. Use our size converter for exact translations between systems.

The +4 method adds 4 inches to your underbust measurement before determining band size. It was created when bras used rigid non-stretch materials. Modern bras are stretchy, so direct measurement is more accurate. Our calculator uses the modern method.

Half-cup sizes like A½, B½, and C½ were pioneered by ThirdLove to address the gap between standard cup sizes. If you consistently feel your cup is slightly too small but the next size up gaps, a half-cup size may be your perfect fit. Currently, only ThirdLove offers half-cup sizing in their bras.