Bra size calculator
Use our bra size calculator to calculate accurate size and measurement values instantly.
Calculator
Estimate bra band and cup from underbust and bust measurements with region-aware output (approximate).
Formula: Cup is estimated from bust-underbust difference; underbust is rounded to a nearest band then mapped to US/UK/EU labels.
What each field means
- Underbust Circumference (cm): Measure snugly around the ribcage directly under the bust.
- Full Bust Circumference (cm): Measure around the fullest part of the bust, tape level and not tight.
- Primary Band System: Enter a valid value for this field.
Estimated Bra Size (US/UK/EU)
Your result will appear here.
Bra Size Guide and Converter
Use this page as a practical fitting companion: calculate a starting size, compare regional labels, and review fit cues before you buy.
Sample Result Snapshot
| Region | Band | Cup |
|---|---|---|
| US / CA | 30 | DD/E |
| UK | 30 (dress code 8) | DD |
| US / CA (+4 method)* | 34 | DD/E |
| UK (+4 method)* | 34 | DD |
| EU (EN 13402) | 70 cm | G |
| FR / BE / ES | 85 cm | G |
| AU / NZ | dress code 10 | DD |
Treat calculator output as a starting estimate. Final comfort and support should be verified with real-world try-on and strap adjustment.
* Some brands still apply the underbust +4 (or +5) rule, which can shift band selection upward.
Measurement Inputs
Bust (example)
92 cm
Band (example)
78 cm
- Bust: relaxed tape around the fullest breast point, standing upright.
- Band: firm tape directly under the bust, snug but not restrictive.
Quick converter sample
Location: US/CA
Band: 28 in
Cup: AA
Why Bra Fit Is Often Off
Sizing inconsistencies are common across labels and countries, so two bras with the same printed size can feel very different. A frequent mismatch is a band that is too loose paired with a cup that is too small.
Center gore lifts
Shoulder strain
Cup spillage
Deep red marks
Band Conversion Matrix
| Band Label | FR/BE/ES | EU | US/UK | AU/NZ |
|---|---|---|---|---|
| XXS | 75 | 60 | 28 | 6 |
| XS | 80 | 65 | 30 | 8 |
| S | 85 | 70 | 32 | 10 |
| M | 90 | 75 | 34 | 12 |
| L | 95 | 80 | 36 | 14 |
| XL | 100 | 85 | 38 | 16 |
| XXL | 105 | 90 | 40 | 18 |
| 3XL | 110 | 95 | 42 | 20 |
| 4XL | 115 | 100 | 44 | 22 |
| 5XL | 120 | 105 | 46 | 24 |
Cup Mapping by Inch Difference
| Bust – Band (in) | US Cup | UK/AU Cup |
|---|---|---|
| <1 | AA | AA |
| 1 | A | A |
| 2 | B | B |
| 3 | C | C |
| 4 | D | D |
| 5 | E or DD | DD |
| 6 | F or DDD | E |
| 7 | G or DDDD | F |
| 8 | H | FF |
| 9 | I | G |
| 10 | J | GG |
| 11 | K | H |
| 12 | L | HH |
| 13 | M | J |
| 14 | N | JJ |
Cup Mapping by Centimeter Difference
| Bust – Band (cm) | EU Cup |
|---|---|
| 10-11 | AA |
| 12-13 | A |
| 14-15 | B |
| 16-17 | C |
| 18-19 | D |
| 20-21 | E |
| 22-23 | F |
| 24-25 | G |
| 26-27 | H |
| 28-29 | I |
| 30-31 | J |
| 32-33 | K |
Difference-to-Cup Visual Chart
Bars show how cup labels scale as bust-minus-band difference increases. Use this as a quick visual, then confirm with physical fit.