Bra Size Calculator
Calculate Bra Size
How to Use This Bra Size Calculator
Finding a perfectly fitting bra is notoriously frustrating because sizing conventions vary wildly between manufacturers and regions. I’ve noticed firsthand that guessing your size often leads to painful wire digging or poor support. To skip the guesswork, use a soft measuring tape and plug your dimensions directly into this calculator. The tool instantly converts your underbust and bust measurements into accurate international sizing across the US, UK, Europe, and Australia.
Bra Size Formulas and Practical Applications
Understanding the standard measurement formula helps you shop smarter, regardless of where you are buying from. Think of your bra size as a mathematical ratio rather than an arbitrary letter. Your cup volume is directly linked to your band length.
Step 1: Find Your Band Size
Your band size is determined by taking your snug underbust measurement and rounding it to the nearest even number. For example, if you measure 31 inches under your bust, your band size is a 32.
Step 2: Find Your Cup Size
Your cup size is simply the mathematical difference between your full bust and your newly calculated band size.
Cup Size Difference = Bust Measurement - Band Size
In practical environments, if your bust measures 35 inches and your band size is 32, the difference is 3 inches. Looking at the standard chart, a 3-inch difference perfectly aligns with a 'C' cup, giving you a final US size of 32C.
Standard Units and Conversion Tables
This calculator relies on the modern sizing method utilized by professional fitters globally. Here is how the inch difference dictates your cup letter across the primary regions:
| Difference (inches) | US Cup Size | Australia Cup Size | UK Cup Size |
|---|---|---|---|
| <1 | AA | AA | AA |
| 1 (2.5 cm) | A | A | A |
| 2 (5.1 cm) | B | B | B |
| 3 (7.6 cm) | C | C | C |
| 4 (10.2 cm) | D | D | D |
| 5 (12.7 cm) | DD/E | DD | DD |
| 6 (15.2 cm) | DDD/F | E | E |
| 7 (17.8 cm) | DDDD/G | F | F |
| 8 (20.3 cm) | H | G | FF |
| 9 (22.9 cm) | I | H | G |
| 10 (25.4 cm) | J | I | GG |
| 11 (27.9 cm) | K | J | H |
| 12 (30.5 cm) | L | K | HH |
| 13 (33 cm) | M | L | J |
| 14 (35.6 cm) | N | M | JJ |
| 15 (38.1 cm) | O | N | K |
| 16 (40.6 cm) | P | O | KK |
| 17 (43.2 cm) | Q | P | L |
| 18 (45.7 cm) | R | LL | M |
Frequently Asked Questions
Does a C cup mean the same thing on every band size?
No, it does not. The cup letter represents a ratio, not a static volume. A 32C has a significantly smaller cup volume than a 38C. This is why "sister sizing" is crucial—if you go down a band size, you must go up a cup size (e.g., from a 34C to a 32D) to maintain the same breast volume.
Should I measure while wearing a bra?
For the most accurate bust measurement, it is generally recommended to measure while wearing an unpadded, well-fitting everyday bra. This ensures your breasts are supported in their natural forward position without artificial lift or compression skewing the numbers.