About this site

This is a single-purpose free tool: two measurements in, a bra size out, with the arithmetic shown. It exists because almost every bra size calculator on the web belongs to a shop, and a shop has a difficult time telling you that the sizing method its own stock is built around is wrong.

The position this site takes

We do not use the +4 method. The band is your underbust measurement rounded to the nearest even inch, not that measurement plus four inches, and the cup is one letter per inch of difference between bust and band.

That is not a novel opinion - professional fitters largely abandoned +4 years ago - but it is still a minority position among online calculators, and it produces results that look startling if you have been sized the old way. A 34B under the old arithmetic is frequently a 30DDD under this one. Both the number and the letter move, which is why we show you the working rather than just the answer. You should be able to check us.

Where the numbers come from

• The sizing arithmetic is two subtractions and a rounding step, and it is covered by an automated test suite that runs on every change. The three worked examples in the test are checkable by hand.
• The conversion tables for US, UK, EU, Australian, Japanese, French and Italian sizing were each verified against more than one independent source, with particular attention above a D cup where the systems stop agreeing and most published charts go wrong.
• The breast weight model is built on a measured figure - one cup size is about 140 mL - and converts volume to weight at a published tissue density of 0.95 g/mL. It reports a range rather than a single number, because published averages for breast volume differ about twofold between populations. What it is confident about is the gap between two sizes; where the whole scale sits varies between people. Its assumptions and its limits are set out in full on its own page, including where it is weakest.

What this site will not do

• Sell you anything, or take a commission. There are no shop links, no affiliate links and no product recommendations anywhere on the site, and there will not be. That is the whole reason the advice here can be blunt.
• Collect your measurements. Everything is calculated in your browser and nothing is transmitted. See the privacy policy.
• Use photographs of bodies. Every diagram on the site is line art, drawn as SVG from the same numbers the calculator uses.

How it is funded

It is not, currently. The running cost is a domain name and static hosting, which is a few hundred rupees a year. If advertising is added later it will be disclosed here and in the privacy policy before it appears, and it will not take the form of product placement or affiliate links dressed up as advice.

Corrections

If a conversion looks wrong to you, please say so - that is the single most useful thing anyone can send us, and errors in conversion tables are exactly the sort that propagate quietly from one site to the next. Write to hello@realbrasizecalculator.com or use the contact page. Please also see the terms of use, which set out what a sizing estimate can and cannot tell you.