Finding the right bra size makes a significant difference to comfort, posture, and confidence. Studies suggest that up to 80% of women wear the wrong bra size — often because sizing varies between brands and because most people were never properly measured. This calculator uses your two key measurements to determine your correct band size and cup size, and also shows your equivalent size in US, UK, European, French, and Australian sizing systems.
All you need is a soft measuring tape and about two minutes. Follow the measurement guide in the calculator for the most accurate result.
Bra Size Calculator
Enter your two measurements below — your band (underbust) measurement and your bust (fullest part) measurement. For best results, measure without wearing a bra or while wearing a non-padded bra.
International Bra Size Conversion Table
Bra sizing systems differ significantly between countries. Use this reference table to convert between the most common international sizing standards.
| US / CA | UK / AU / NZ | EU (DE/NL/SE) | FR / BE / ES | IT | JP |
|---|---|---|---|---|---|
| 28 | 28 | 60 | 75 | 0 | 55 |
| 30 | 30 | 65 | 80 | 1 | 60 |
| 32 | 32 | 70 | 85 | 2 | 65 |
| 34 | 34 | 75 | 90 | 3 | 70 |
| 36 | 36 | 80 | 95 | 4 | 75 |
| 38 | 38 | 85 | 100 | 5 | 80 |
| 40 | 40 | 90 | 105 | 6 | 85 |
| 42 | 42 | 95 | 110 | 7 | 90 |
| 44 | 44 | 100 | 115 | 8 | 95 |
Note: Cup letters (A, B, C, D, etc.) remain the same across US, UK, and Australian sizing. European and French cup sizing differs slightly — see the cup conversion section below.
| US / UK / AU Cup | EU Cup | FR Cup | IT Cup | JP Cup |
|---|---|---|---|---|
| AA | AA | AA | AA | AAA |
| A | A | A | A | AA |
| B | B | B | B | A |
| C | C | C | C | B |
| D | D | D | D | C |
| DD / E | E | E | DD | D |
| DDD / F | F | F | E | E |
| G | G | G | F | F |
| H | H | H | G | G |
How Is Bra Size Calculated?
Bra size is made up of two components: the band size (a number) and the cup size (a letter). The band size relates to your ribcage measurement, and the cup size is determined by the difference between your bust measurement and your band measurement.
Measure your underbust (ribcage directly below the bust) in inches.
If the result is an odd number, round up to the next even number.
Example: 31 inches → Band size 32
Step 2 — Find your cup size:
Subtract your band size from your bust measurement (fullest part).
Each inch of difference = one cup size.
0″ = AA, 1″ = A, 2″ = B, 3″ = C, 4″ = D, 5″ = DD/E, 6″ = DDD/F, 7″ = G, 8″ = H
Example: Underbust 31″ → Band 32 · Bust 36″ · Difference = 36 − 32 = 4″ → Cup D
Result: 32D
What Are Sister Sizes?
Sister sizes are bra sizes that have exactly the same cup volume but a different band size. When you go up one band size, you go down one cup letter — and vice versa. For example, 34C, 36B, and 32D all contain the same cup volume. If your exact size is sold out or unavailable, a sister size is the next best option, though the fit will feel slightly different because the band will be looser or tighter.
Signs Your Bra Fits Correctly
Common Fitting Problems and Solutions
How Often Should You Get Remeasured?
It is recommended to remeasure every 6–12 months, and also after significant weight changes (gain or loss of more than 10 lbs / 5 kg), pregnancy, breastfeeding, surgery, or if your current bras suddenly feel uncomfortable. Bra size can change considerably throughout life, and many women find their size has changed without realising it.
Frequently Asked Questions
Why do different brands fit differently even in the same size?
There is no universal industry standard for bra sizing, so a 34C from one brand may fit completely differently from a 34C from another. Factors include the cut of the cup, the stretch of the band fabric, and the shape of the underwire. Always try bras on when possible, and use the size from this calculator as a starting point rather than an absolute rule.
Should I measure with or without a bra on?
For the most accurate result, measure without wearing a bra, or while wearing a well-fitting non-padded bra. Padded or push-up bras will artificially increase your bust measurement and give you an inflated cup size reading.
What is the difference between US and UK sizing?
The band numbers in US and UK sizing are identical — a UK 34C is the same band measurement as a US 34C. The difference arises in larger cup sizes: in the UK, the cup sequence goes A, B, C, D, DD, E, F, FF, G — whereas in the US it goes A, B, C, D, DD (or E), DDD (or F), G. For everyday sizes up to D cup, the two systems are interchangeable.
My measurements fall between two sizes — which should I choose?
If you are between band sizes, try both and fasten the bra on the loosest hook. As the band stretches over time, you can progress to the middle and then the tightest hook, extending the life of the bra. If you are between cup sizes, try both and assess which gives you better coverage and shape without spillage or gaping.