Bra Size Calculator – Find Your Perfect Fit in Inches
Most women are wearing the wrong bra size, and many do not even know it.
An estimate, not a fitting. Use this result as your starting size — trying sister sizes around it helps you find the perfect fit.
| Difference (bust − band) | Cup size |
|---|---|
| 0″ or less | AA |
| 1″ | A |
| 2″ | B |
| 3″ | C |
| 4″ | D |
| 5″ | DD |
| 6″ | DDD |
| 7″ or more | G |
Sister sizes share the same cup volume: if 34B feels tight in the band, try 36A; if the band feels loose, try 32C.
Straps that dig in, a band that rides up your back, cups that gape or spill over: these are all signs that your size has changed or was never quite right.
The good news is that finding your starting size is simple, and you can do it at home in two minutes.
Our free bra size calculator needs just two measurements in inches: one around your ribcage and one around the fullest part of your bust.
From those two numbers it works out your band size and your cup size, and gives you a clear result like 34B.
It is a starting point, not a final verdict, so think of it as a friendly guide that points you to the right fitting room.
Grab a soft tape measure, stand in front of a mirror, and let us find your fit together.
How to Use
Example
Let us work through a real example. Suppose your band measurement is 34 inches and your bust measurement is 36 inches.
First, the band: 34 is already an even number, so your band size stays 34.
Next, the cup: subtract the band from the bust, 36 − 34 = 2 inches, and a 2-inch difference means a B cup.
Put them together and your estimated size is 34B.
If 34 felt a little snug around the ribs, its sister size would be 36A, which holds the same cup volume on a looser band.
If the band felt loose, you could try 32C instead. One more quick example: a band of 33 inches rounds up to 34.
And a bust of 37 inches gives a 3-inch difference, which is a C cup, so the result is 34C.
The Bottom Line
A well-fitting bra changes how your clothes sit, how your posture feels, and how comfortable you are all day long.
It should never pinch, ride up, or leave marks, and the band should do most of the supporting, not the straps.
This calculator gives you a solid starting size from two simple measurements, and from there the fitting room does the rest.
Try your result first, then its sister sizes, and judge by comfort rather than by the letter on the label.
Sizes vary between brands too, so the number that fits you in one shop may be one step different in another, and that is completely normal.
Frequently Asked Questions
How accurate is this bra size calculator?
It gives a good estimate based on the standard method: band size from your underbust, cup size from the difference between bust and band. Most people land within one size of their best fit.
Why is my band size rounded to an even number?
Bra bands are sold in even numbers only: 32, 34, 36, and so on. If your tape reads an odd number like 33, we round up to 34.
What are sister sizes?
Sister sizes are different band and cup combinations that hold the same cup volume. For example, 34B, 36A and 32C are sister sizes.
How do I know if a bra fits properly?
Check four things. The band should sit level around your body and feel snug on the loosest hook. The centre should sit flat, the cups should hold you fully, and the straps should stay put without digging in.
How often should I re-measure my bra size?
At least once a year, and any time your body changes. Weight changes, pregnancy, breastfeeding and a new exercise routine can all change your size.
Does the calculator work for all body types?
The maths works for most adults, but it is a general guide, not a professional fitting. Very full busts or an unusual shape may need an in-person fitting to get the best result.
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