Bra Size Calculator
Find your bra size and cup size from band and bust measurements.
This bra size calculator converts a band measurement and a bust (over-bust) measurement into a standard bra size, using the same bra measurement chart most lingerie retailers use to size their products. It works as a bra cup size calculator for anyone unsure how to size a bra correctly, whether they're shopping online or determining bra size after a body change.
Enter your band measurement (snug, under the bust) and your bust measurement (around the fullest part), and the calculator returns your estimated size, such as 34B or 36DD.
Worked Calculation Examples
| Scenario | Result | Calculation Step |
|---|---|---|
| 32 in band, 36 in bust | 32D | Difference = 36 − 32 = 4 in → D cup. Band size = 32. Result: 32D. |
| 36 in band, 39 in bust | 36C | Difference = 39 − 36 = 3 in → C cup. Band size = 36. Result: 36C. |
How to Measure Bra Cup Size
Cup size is determined by the difference between the bust measurement and the band measurement, not by the bust measurement alone. A 1-inch difference is typically an A cup, 2 inches a B cup, 3 inches a C cup, and so on up the bra size chart - so two people with the same bust measurement can have different cup sizes if their band measurements differ.
Bust Size to Cup Size Chart Basics
Because sizing conventions vary slightly between US, UK, and international brands, a bust size to cup size chart from one retailer may label the same measurements differently than another. This determining bra size calculator uses the common US sizing convention as a starting point - it's worth trying on a size within one band and one cup of the result, since fit also depends on the bra's cut and material.
How to Use the Bra Size Calculator
- Open the Bra Size Calculator and enter the values requested in the input fields.
- Check the units, percentages, dates, or time periods before reading the answer.
- Review the instant result and adjust any value to compare another scenario.
- Use the formula, example, and FAQs below to understand how the bra size calculator works.
Frequently Asked Questions
How do I measure my bra cup size?
Measure snugly around your band (under the bust) and around the fullest part of your bust, then find the difference - each inch of difference corresponds to roughly one cup size on the bra size chart.
How do you calculate bra size?
Round the band measurement to the nearest even number for your band size, then use the difference between bust and band measurements to determine your cup letter.
What if my band and cup sizes fall between two values?
Try the closest standard sizes on both sides - fit varies by brand and style, so a bra measurement chart gives a strong starting point rather than an exact guarantee.
How do I use this bra size calculator?
Enter the known values, review the units or settings, and the calculator updates the result instantly. The formula and example on this page show how the answer is produced.
What does the Bra Size Calculator calculate?
Find your bra size and cup size from band and bust measurements. It is designed for fast browser-based calculations without sign-up, downloads, or manual spreadsheet setup.
What formula does this bra size use?
The formula is: Cup Size ≈ Bust Measurement − Band Measurement (each inch of difference = one cup size). The modern band-and-cup bra sizing system was patented by S.H. Camp and Company in 1933, introducing standardized cup lettering (A, B, C, and so on) for the first time in an industry that had previously sized bras more like generic small/medium/large garments - the roughly one-inch-per-cup-size convention this formula reflects has remained the basic industry standard for nearly a century since.
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Last updated: September 27, 2026.