Bra Size Calculator

Comprehensive Guide to Bra Sizing

Studies suggest that upwards of 80% of women wear the wrong bra size, leading to discomfort, poor posture, and inadequate support. The traditional "plus four" measurement method created decades ago is wildly outdated and forces many into bands that are too loose and cups that are too small.

The Bra Size Calculator utilizes modern, direct-measurement techniques to accurately determine your band and cup size, translating those measurements across US, UK, and European sizing standards.

How to Use the Bra Size Calculator

You will need a soft, flexible measuring tape. For the most accurate results, take these measurements while unbraed or wearing a non-padded, well-fitting bralette.

1. Measure Your Underbust (Snug): Wrap the tape directly under your breasts, where the bra band normally sits. Pull it comfortably snug. Enter this measurement in inches or centimeters.
2. Measure Your Overbust (Standing): Wrap the tape around the fullest part of your breasts. The tape should be level but not pulled tight—it should just lightly rest on the tissue.
3. Calculate: The tool will analyze the difference between these two measurements to output your exact cup and band size.

The Formula

Modern bra sizing operates on a very simple mathematical principle: The band size is your physical underbust measurement, and the cup size is the difference between your overbust and your underbust.

Determining Band Size

In modern sizing, your band size is simply your snug underbust measurement rounded to the nearest even number.

Underbust: 31.5 inches -> Round to 32 Band
Underbust: 33 inches -> Round to 34 Band

Determining Cup Size

Subtract your underbust measurement from your overbust measurement. Every 1-inch difference generally equates to one cup size.

Difference = Overbust - Underbust

1 inch difference = A Cup
2 inch difference = B Cup
3 inch difference = C Cup
4 inch difference = D Cup
5 inch difference = DD (or E) Cup
...and so on.

Practical Examples

Scenario 1: Standard Calculation

• Underbust: 34 inches
• Overbust: 37 inches
• Difference: 37 - 34 = 3 inches.
• Result: Size 34C.

Scenario 2: The Sister Size Concept If a 34C feels too tight in the band, you might try a 36 band. But if you go up a band size, you must go down a cup size to maintain the exact same volume of breast tissue.

• Sister Size Up: 36B (Looser band, same cup volume)
• Sister Size Down: 32D (Tighter band, same cup volume)

Conclusion

A well-fitting bra can radically alter how your clothes fit and eliminate chronic shoulder and back pain. Stop relying on outdated "+4" sizing methods. Use this calculator to find your mathematically accurate baseline size, and use the concept of "Sister Sizing" to fine-tune your fit across different brands.

Disclaimer: Bra sizing is not perfectly standardized across the global garment industry. Different brands use different grading rules and stretch fabrics. This calculator provides your mathematically accurate baseline size, but you may still need to adjust up or down a size depending on the specific manufacturer's cut and your unique breast shape.