Method
The modern starting band rounds underbust to the nearest even inch; rounded bust-minus-band difference indexes a common retail cup sequence.
Everyday worksheet
Bra Fitting Starting-Size Calculator
Estimate a common retail starting size from snug underbust and full-bust measurements, with sister sizes and method caveats.
The calculation runs locally. Results include the intermediate values, unit conversions and assumptions needed to audit the answer.
Method, assumptions and practical use
How the Bra Fitting Starting-Size Calculator works
The modern starting band rounds underbust to the nearest even inch; rounded bust-minus-band difference indexes a common retail cup sequence. Inputs stay in this browser, and the result table exposes conversions and assumptions for independent checking.
Interpret the result
The output is a fitting starting point; sister sizes trade a smaller band for a larger cup letter or the reverse.
Check the assumptions
Brands, styles, cup shape, stretch, asymmetry and regional lettering vary materially; no universal retail bra formula exists.
Local calculation
Everything runs in this browser. Inputs are not sent to an external calculator.
Rounding
Displayed values may be rounded for readability while calculations use full floating-point precision unless the tool explicitly uses exact integers.
Scope
Brands, styles, cup shape, stretch, asymmetry and regional lettering vary materially; no universal retail bra formula exists.
Simple by design
Three steps to a clearer number.
Enter your details
Use realistic values in each field. You can change them anytime.
Calculate instantly
The formula runs locally, so there is no account or waiting time.
Use the result
Treat the answer as a practical estimate for your next decision.