What is the Bra Size Calculator?
Finding the right bra size can be notoriously difficult due to variations in body types, brand inconsistencies, and vastly different sizing systems used around the world. The Bra Size Calculator is designed to accurately estimate your bra size based on your exact bust and band measurements (or underbust measurements).
Alternatively, the built-in size converter allows you to instantly translate a known, well-fitting bra size from one region (like the US or UK) into the correct size for shopping internationally (such as the EU, Australia, or France).
How to Measure Your Bra Size
To use the measurement calculator, grab a soft measuring tape and follow these steps. For the most accurate results, perform these measurements while unassisted, standing straight, and wearing a non-padded, properly fitted bra.
- 1. Band Size (Underbust): Wrap the measuring tape firmly (but not too tightly) directly underneath your breasts, around your ribcage. Ensure the tape is level across your back. This determines your frame size.
- 2. Bust Size (Fullest Part): Wrap the tape loosely around the fullest part of your breasts. Do not pull the tape tight; it should rest lightly against your skin without indenting the breast tissue.
The Formula / The Science of Bra Sizing
Bra sizing historically uses two key metrics: the numerical band size and the alphabetical cup size. The cup size is determined by the difference between your bust circumference and your band circumference.
Cup Size = Bust Measurement (inches) − Band Size (inches)
Example:
Bust (37") − Band (34") = 3 inches difference.
A 3-inch difference typically corresponds to a C Cup.
The "+4 Method" vs. Modern Sizing
You may have heard of adding 4 or 5 inches to your underbust measurement to get your band size. This older technique, known as the "+4 method," was popularized before elastic fabrics were common. Today, modern sizing methods usually base the band size directly on the underbust measurement (rounded to the nearest even number). Our calculator provides both the modern result and the legacy "+4" result for your reference, as some older brands still use the latter.
Frequently Asked Questions
A well-fitting bra should have a band that lies horizontally across your back without riding up. The center gore (the piece between the cups) should sit flat against your sternum. The cups should fully encapsulate the breast tissue without overflowing (quad-boob) or wrinkling, and the straps shouldn't dig in or fall off.
Many women settle for incorrect sizes due to lack of standardization among manufacturers, body changes over time (weight loss, pregnancy, age), or relying on the outdated "+4 measurement method." Studies consistently show that the most common mistake is wearing a band that is too large and a cup that is too small.
They are the same for band sizes and smaller cup sizes (AA through D). However, past a D cup, the systems diverge. The UK uses double letters extensively (DD, E, F, FF, G), whereas the US uses DDD, G, H, I, etc. Our calculator accurately handles this conversion for you.
Sister sizes are bra sizes that share the exact same cup volume, but differ in the band length. If you change your band size, you must change the cup size inversely to keep the same cup volume. For example, a 34C has the same cup volume as a 36B or a 32D.
It is recommended to check your bra size every 6 to 12 months. Hormonal fluctuations, weight changes, aging, and pregnancies can all affect your body shape, making your old, comfortable bras less supportive.