How to use it
- Enter your underbust measurement in inches.
- Enter your bust measurement in inches.
- Click Calculate to see band size and cup index.
What it does – The Bra Size Calculator takes your underbust and bust measurements (in inches) and instantly returns the US band size and the cup‑size index (A = 1, B = 2, …). The band size follows the standard rule: add 4 inches if your underbust is an even number, or 5 inches if it’s odd. The cup index is the rounded difference between bust and the computed band size, each inch moving you up one cup letter. Knowing both numbers lets you shop with confidence, compare brands, and avoid costly returns. Read the result: a band size like 34 in and a cup index of 2 means a 34B. Use the index to pick the matching letter in any sizing chart. You can also save the result for future reference or share it with a tailor.
Pro tips
- Measure underbust at the smallest point, keeping the tape snug but not tight.
- Round the difference to the nearest whole inch before assigning the cup index.
- If your underbust is odd, remember to add 5 inches—not 4—to get the band size.
- Double‑check both measurements before submitting to avoid common off‑by‑one errors.
Real-life examples
- A college student buying her first bra online wants the correct size to avoid returns.
- A plus‑size shopper comparing brands needs a reliable band and cup reference.
- A tailor needs exact measurements to alter a custom‑made bra.
Case study
Maria measured 29 in underbust and 34 in bust. The calculator gave her a band size of 34 in and cup index 1 (34A). She ordered the recommended size and the bra fit perfectly, eliminating the need for returns.