Bra Size Calculator

Written by Great Medico

Updated September 25, 2026 •2 min read

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When you are trying to turn underbust and bust measurements into an approximate multi-region bra size, rough mental math can become surprisingly error-prone. The Bra Size Calculator turns the specific values on this page into a transparent estimate, then gives you enough context to see whether the result changes because of the formula, the units, or an assumption you entered.

What this calculator does

The calculator’s primary output is bra size estimate. It also exposes useful supporting values such as US, UK, EU. Its scope is deliberately narrow: it uses the fields shown for Bra Size and does not silently add outside prices, specifications, measurements, or assumptions that are not present on the page. Where the page uses a chart, threshold, lookup, or heuristic rather than a continuous physical equation, the result should be read as a category or recommendation produced by that current model.

How to use it

Enter Underbust and Bust. Use the page’s unit selectors rather than converting dimensions mentally. If the result is a size category, treat it as a starting point; if it is a cutting or yardage quantity, round practical purchases upward when a shortage would be costly.

How the calculation works

The current sizing model rounds underbust to an even US band and maps bust-minus-underbust difference to a cup letter. It also shows approximate UK and EU equivalents from the same measurements.

Example

A quick hand-check starts with Underbust (32 in); Bust (36 in), the calculator returns 32D for bra size estimate. Change one of those inputs and the result should move in the direction implied by the formula or lookup above. That is a useful way to catch a unit mistake or an unrealistic assumption before relying on the estimate.

How to interpret the result

For the Bra Size Calculator, treat the bra size estimate as a sizing, cutting, or material-planning starting point for the measurements entered, not as a promise of final fit or finished dimensions. When comparing two Bra Size Calculator scenarios, keep every unchanged input identical so the difference in results comes from the factor you actually want to test.

Limitations and notes

For the Bra Size Calculator, bra sizing is not standardized across brands or countries, and cup volume changes with band size. Use the result as a starting point, then check the manufacturer chart and fit indicators or try nearby sister sizes.