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How US Sizing Actually Works
US sizing pairs a band number in inches with a cup letter, where the cup letter comes from the gap between your band and bust measurement.
Because it’s the default system here, the main calculator, sister-size tool, and every guide on this site already speak US sizing natively. No conversion needed.
Convert Your Size
Use the calculator above to see your size across all 7 systems this site supports, US included. If you already know your size in another system, enter it into the Global Bra Size Converter instead of doing the math by hand.
Getting an Accurate Starting Point
No conversion is more accurate than the measurement it’s based onHow to Measure covers the exact technique this calculator assumes, and the Sister Size Calculator is worth trying if your first result doesn’t feel quite right.
A Worked Example for the United States
Say your underbust measures 36 inches and your bust measures 40 inches. A US 36C.
Converted to the United States’s system, that becomes roughly 36″ C using the formula above. Run your own numbers through the calculator on this page rather than eyeballing the conversion. Small rounding differences near a size boundary can shift the result by a full cup letter.
Shopping Locally vs. Importing in the United States
American shoppers usually have the easiest time of this group. Most national chains fit-check in person, and exchanges are typically free and fast if the first size feels off.
Common Sizing Mistakes Shoppers Make in the United States
A common mistake among US shoppers is trusting a decade-old size without re-measuring. Bodies change enough over years that an old number quietly stops being accurate.
Another frequent slip is skipping the band measurement and shopping by cup letter alone. Band size does most of the actual support work, not the cup.
A Note on Retail Fitting in the United States
Most US mall-based retailers offer free, no-appointment-needed fittings, making an in-person check the fastest way to confirm a converted size before buying.
Buying From the US If You’re Not Based There
US-based online retailers often ship internationally, but customs fees and longer delivery windows are worth factoring in before ordering. A size mistake becomes more expensive to return when it has to cross a border twice.
Why the US Never Standardized Further
Despite being one of the most-shopped markets in the world, the US never adopted a single mandatory sizing standard the way some regulated industries have. Bra sizing has stayed a voluntary industry convention, which is exactly why brand-to-brand variation is so common here specifically.
Shopping Across State Lines
Since sizing isn’t regulated at a state level, there’s no regional variation to worry about within the US itself. A size bought in one state means exactly the same thing bought in another, unlike some countries with regional retail differences.
A Practical Rule for First-Time Orders
If you’re ordering from a US brand for the first time and can’t try before buying, ordering your calculated size plus checking that specific product’s own reviews for true-to-size feedback is more reliable than trusting the brand’s general reputation alone.
