USA Bra Size Calculator with Measurement Chart

The USA bra sizing system differs significantly from other countries due to its unique "plus-four" method for calculating band sizes. This approach was historically based on the assumption that bra bands should be stretched during wear, but modern bra fitting emphasizes this approach may not provide optimal support for everyone.

For example, if your underbust measures 30 inches (even), your band size would be 34 (30 + 4). If your overbust measures 35 inches, the cup difference is 5 inches, which corresponds to a DD cup in the American system. Therefore, your size would be 34DD.

The band size in the USA system (28, 30, 32, 34, 36, 38, 40, 42, 44, etc.) should provide most of your bra's support, typically accounting for 80% of the total support. The cup size is determined exclusively by the difference between your overbust and underbust measurements.

The American cup progression is: AA, A, B, C, D, DD (also called E), DDD (also called F), DDDD (also called G), H, I, J, K, L, M, N, O and beyond for extremely large cup sizes.

Understanding sister sizes is valuable for several reasons. If a bra fits perfectly in the cups but feels loose in the band, try going down a band size and up a cup size. Conversely, if the band is too tight but cups fit well, try going up a band size and down a cup size.

• Band Support: The band should sit horizontally across your back, parallel to the ground. It should be snug enough to provide support without digging into ribs or causing marks. The band provides the majority of a bra's support force.
• Cup Coverage: Breasts should be completely contained within the cups with no spillage or overflow. Check the sides, top, and under the arms for any breast tissue escaping the cup boundaries. The center gore should lie flat against your sternum between your breasts.
• Strap Position: Straps should sit securely on your shoulders without slipping off. They should be snug but not so tight that they dig in or cause pain. Use the band size to provide most of the support, with straps as secondary support only.
• Underwire Placement: If wearing an underwired bra, the wires should rest against your ribcage at the crease where your breast naturally ends. They should never sit on breast tissue or dig into your armpits.
• Hook Position: Choose a bra that fits comfortably on the loosest hook (usually the last column). This allows you to gradually tighten to the middle and then tightest hooks as the elastic stretches with wear and washing.
• Movement and Comfort: Raise your arms, bend forward, and move around to test the fit. Your breasts should stay in place, the band shouldn't ride up, and straps shouldn't slip. You should feel supported throughout the day.
• Regular Fitting: Get professionally fitted at least once yearly or whenever you experience significant weight changes, hormonal fluctuations, pregnancy, or breastfeeding. Breast size changes more frequently than many women realize.

If your bra band rides up your back during the day, the band size is typically too large. Try sizing down one band size and going up one cup size using your sister size. The band should remain horizontal and provide most of your bra's support.

When breast tissue spills over the top, sides, or under-arms of the bra, this indicates your cup size is too small. Increase your cup size by one or two letters. Make sure you're scooping all breast tissue into the cups when putting on your bra, as improper placement can cause apparent overflow.

Empty space or wrinkled fabric in your cup means the cup size is too large. Try decreasing your cup size by one letter. However, some bra styles don't work well with all breast shapes, so consider trying different style brands before changing sizes.

Painful strap indentations suggest the band isn't tight enough and your straps are compensating by bearing too much weight. Try sizing down in the band. If straps slip on your shoulders, your band is too loose or you may have sloped shoulders requiring an underwire with forward-set straps.

Bulging or spilling of back tissue often indicates the band is too tight. Try sizing up one band size and down one cup size using sister sizing. Alternatively, you may need a different cup depth or wire width.

The plus-four method was developed decades ago when bra bands were made from less elastic materials and bras were meant to stretch significantly. Modern bra construction uses more elastic materials, and many fitters now believe accurate band fit should be based on actual underbust measurement with minimal adjustment.

If you find yourself between sizes or if traditional sizing doesn't feel right, experiment with the modern approach of using your actual underbust as your band size. Many women find significantly better support and comfort this way.