About BraCalc

Last reviewed on 28 April 2026.

Who BraCalc is for

BraCalc is a free reference site for anyone who needs to translate two body measurements — underbust and full bust — into a bra size that actually fits. That covers a wide range of readers: people shopping online and trying to read a foreign size chart, people who have measured themselves at home for the first time, people whose body has changed and who suspect their old size no longer applies, and people troubleshooting fit problems with a bra they already own.

The site is not a retailer. Nothing is for sale here, and BraCalc has no inventory, no stock-keeping fees, and no commercial pressure to push a particular size, brand, or style on a reader. The only goal is to help a reader land on a starting size and a small set of useful neighbouring sizes (sister sizes) to try.

What the site covers

The core of BraCalc is the calculator, which takes an underbust and an overbust measurement and returns an estimated bra size in six widely-used systems: US, UK, EU, FR, AU, and JP. Around the calculator, the site provides:

• A sister-size matrix showing which sizes share the same cup volume but differ in band tension — with a longer explanation in sister sizes explained.
• An international size converter that maps a known size in one system to its closest equivalent in another.
• A fit test that links common visible problems (band riding up, cups gapping, gore not lying flat) to the change of size or shape that usually fixes them, paired with deeper reading on band vs cup and bra styles.
• A library of per-size guides under /size/ covering specific band-and-cup combinations from 28 through 48 in the most common cup letters.

Editorial approach

BraCalc takes a deliberately narrow stance: every page is about bra sizing, fit, or the relationship between the two. The tone is practical and matter-of-fact. The site does not run sponsored content, does not accept payment to recommend a particular brand, and does not pretend that a measurement-based estimate is a substitute for trying a bra on. Sizing systems vary between manufacturers; the calculator and the size guides give a sensible starting point, not a guaranteed perfect fit.

Editorial copy on the site is written and reviewed in plain English, with the goal of being usable by a reader who has never thought about band tension, cup volume, or sister sizes before. Where a topic touches health (for example, sizing changes during pregnancy, after surgery, or during weight change), pages stop at general information. They do not give medical advice, and they signpost a qualified fitter or clinician where one is appropriate.

How the sizing data is produced

The calculator is built on a transparent rule set: the band size is chosen from the underbust measurement using a standard inch-based rounding range, and the cup is derived from the difference between the overbust and the underbust, with one inch of difference equating to roughly one cup letter. International equivalents are looked up against published sizing tables for each region — the EU and FR systems are centimetre-based, the UK system shares band numbers with the US but diverges from D up, and AU and JP each use their own conventions. None of the values are randomised, and the same inputs always return the same outputs.

Sister sizes are generated mechanically from the same rule that bra fitters use: dropping one band size and adding a cup letter (or vice versa) preserves cup volume while changing band tension. The matrix on the home page shows that relationship directly so a reader can verify it rather than take it on trust.

How content is reviewed and updated

Substantive pages on BraCalc carry a "Last reviewed" date so readers can see how recently a page was checked. When sizing standards or widely-used regional charts change, or when readers point out a rounding case that the calculator handles awkwardly, the relevant pages are updated and the review date is bumped. Minor copy edits do not necessarily change the date; substantive updates to information do.

Privacy and ads

BraCalc uses analytics to understand which pages readers find useful and may run advertising through Google AdSense to keep the site free. Both are explained in the Privacy Policy and Cookie Policy. Measurements entered into the calculator are processed in the reader's browser and are not transmitted to BraCalc as part of the calculation.

Getting in touch

Corrections, suggestions, and questions are welcome — see the Contact page for the email address. If a calculation looks wrong for a particular pair of measurements, sending the underbust and overbust values along with the size returned helps a great deal in tracking down the issue.