Bra Size Calculator — Accurate US, UK, EU & International Sizing
Free online Bra Size Calculator. Find your true, comfortable bra size using snug underbust and bust measurements. Includes instant US, UK, EU, and Australian size conversions and sister size recommendations.
How to use this calculator
👉 Fill in the boxes below and your answer appears instantly — no maths needed, we do it all for you! 🎉
In plain English — what does this do?
📊 A helper for daily life! Things like working out your age, how much to tip, what a sale price is, or how long until your birthday. Quick and easy answers for real life!
A Bra Size Calculator determines your precise brassiere band and cup size based on two anatomical measurements: snug underbust circumference and full bust circumference. Studies show that over 80% of women wear an incorrect bra size, leading to back pain, poor posture, and strap slippage. This calculator provides accurate sizing across US, UK, European, and Australian standards.
Directly below breasts, snug against ribcage.
Around the fullest part of bust, level all around.
Your Recommended Bra Size
Band provides 80% of bust support; cups should encase breast tissue without spilling.
EU Size
70D
AU / NZ Size
10D
Sister Size (Tighter)
30DD
Sister Size (Looser)
34C
What is Bra Size Calculator — Accurate US, UK, EU & International Sizing?
A Bra Size Calculator determines your precise brassiere band and cup size based on two anatomical measurements: snug underbust circumference and full bust circumference. Studies show that over 80% of women wear an incorrect bra size, leading to back pain, poor posture, and strap slippage. This calculator provides accurate sizing across US, UK, European, and Australian standards.
How to use it
- 1️⃣ Wear an unpadded, non-pushup bra or measure braless while standing straight.
- 2️⃣ Measure your snug underbust directly under your breasts with a flexible tape measure held parallel to the ground.
- 3️⃣ Measure around the fullest part of your bust without pulling the tape too tight.
- 4️⃣ Select your measurement unit (Inches or Centimeters).
- 5️⃣ Instantly view your calculated band size, cup letter, international equivalents, and sister sizes.
Formula & Variables
Variable Definitions:
💡 See it in action — a real example
📊 Bust Difference to Cup Size Chart
Standard progression of cup letters based on bust-minus-band difference in inches.
| Difference (Inches) | US Cup Size | UK Cup Size | EU Cup Size | Cup Volume Description |
|---|---|---|---|---|
| Less than 1 inch | AA | AA | AA | Very Small / Petite |
| 1.0 inch (2.5 cm) | A | A | A | Small |
| 2.0 inches (5.1 cm) | B | B | B | Medium-Small |
| 3.0 inches (7.6 cm) | C | C | C | Medium |
| 4.0 inches (10.2 cm) | D | D | D | Medium-Full |
| 5.0 inches (12.7 cm) | DD / E | DD | E | Full |
| 6.0 inches (15.2 cm) | DDD / F | E | F | Extra Full |
| 7.0 inches (17.8 cm) | G | F | G | Very Full |
| 8.0 inches (20.3 cm) | H | FF | H | Substantial |
* UK and US sizing diverge significantly beyond DD cups.
📊 International Band Size Equivalent Chart
Comparison of band sizes across major geographic apparel manufacturing systems.
| Underbust (Inches) | Underbust (cm) | US / UK Band | EU / Japan Band | FR / ES Band | AU / NZ Band |
|---|---|---|---|---|---|
| 28 – 29 in | 70 – 74 cm | 30 | 65 | 80 | 8 |
| 30 – 31 in | 75 – 79 cm | 32 | 70 | 85 | 10 |
| 32 – 33 in | 80 – 84 cm | 34 | 75 | 90 | 12 |
| 34 – 35 in | 85 – 89 cm | 36 | 80 | 95 | 14 |
| 36 – 37 in | 90 – 94 cm | 38 | 85 | 100 | 16 |
| 38 – 39 in | 95 – 99 cm | 40 | 90 | 105 | 18 |
| 40 – 41 in | 100 – 104 cm | 42 | 95 | 110 | 20 |
* EU band sizes represent actual metric ribcage measurement in cm minus approx 5cm for elasticity.
❓ Common questions
- Why do so many women wear the wrong bra size?
- Most women wear a band that is too loose and cups that are too small. Many traditional department stores still use the outdated '+4 system' designed decades ago for non-stretch fabrics, resulting in inadequate support from the band and painful strap gouging.
- What are 'Sister Sizes' and how do they work?
- Sister sizes are bra sizes that hold the exact same cup volume despite different band numbers. If a band feels too tight, go UP one band size and DOWN one cup letter (e.g., 34C to 36B). If a band is too loose, go DOWN one band size and UP one cup letter (e.g., 34C to 32D).
- How tight should a bra band feel when new?
- A new bra should fit firmly and parallel around your ribcage on the loosest hook. As the elastic band stretches naturally over months of wear, you can move to the middle and tightest hooks to preserve support.
- Should I measure while standing or leaning forward?
- For the most accurate result, especially for softer breast tissue, measuring while standing and taking an average with a 90-degree leaning measurement helps capture full breast projection.
- How often should I recalculate my bra size?
- You should remeasure every 6 to 12 months, or whenever you experience weight fluctuations of 5–10 lbs, hormonal changes, pregnancy, or changes in exercise routine.