General
Bra Size Calculator
Calculate your accurate bra size using band and bust measurements for a proper fit.
Reviewed by the calculator.uk.com Team · Last reviewed 4 July 2026 · Our methodology
Enter your measurements to calculate your bra size
The bra size calculator uses two key measurements to determine your ideal bra size: the band size and the bust size. The calculation process involves several steps to ensure accuracy:
Band Size Calculation
The band size is rounded to the nearest even number, as bra bands typically come in even-numbered sizes. This measurement forms the numerical part of your bra size.
Cup Size Determination
The cup size is calculated by finding the difference between your bust and band measurements. Each inch of difference corresponds to a cup size, starting with AA for less than 1 inch, then A, B, C, and so on.
Taking accurate measurements is crucial for finding your correct bra size. Here's how to measure properly:
Band Size Measurement
Measure around your ribcage just under your breasts, where the band would sit. Keep the measuring tape level and snug but not tight. This measurement in inches is your band size.
Bust Size Measurement
Measure around the fullest part of your bust while wearing an unpadded bra. Keep the measuring tape level and somewhat loose to avoid compression.
1. Why does my calculated size seem different from what I usually wear?
Many people wear the wrong bra size without realizing it. The calculated size might seem different because it's based on your actual measurements rather than what you're used to wearing. It's worth trying the calculated size as it may provide better support and comfort.
2. Should I round my measurements?
Enter your exact measurements into the calculator. The calculator will handle any necessary rounding, particularly for the band size which needs to be an even number.
3. What if my size isn't available in stores?
If your calculated size is hard to find in regular stores, consider specialty lingerie shops or online retailers that offer a wider range of sizes. Some brands also offer sister sizes which might be more readily available.
4. How often should I measure my bra size?
It's recommended to measure your bra size every 6-12 months, or if you experience significant weight changes, pregnancy, or other body changes that might affect your measurements.
5. What is the scientific source for this calculator?
Bra sizing is not governed by a scientific standards body; it follows a sizing convention developed within the lingerie industry, in which the band size is derived from the underbust measurement and the cup size from the difference between bust and underbust measurements. Because manufacturers apply this convention somewhat differently, and body shapes vary in ways a single formula cannot capture, the calculated size is a reliable starting point rather than a guaranteed fit, which is why professional fitters recommend trying on a few neighboring sizes.