Bra Size Calculator
Enter your measurements for a quick starting size. This is an estimate designed to help you shop smarter.
How this bra size calculator works
This calculator uses two core measurements: your snug underbust and your full bust. From there, it estimates a band size and cup size based on common US/UK fitting conventions. It is intended as a practical starting point—not an absolute final answer.
Many people wear the wrong bra size for years simply because sizing can vary by brand, style, and fabric. A calculator helps narrow your choices quickly so you can start trying sizes that are much closer to your best fit.
Step 1: Estimate your band size
Your band size is based on your underbust measurement. In this tool, we convert your measurement to inches (if needed), then round to the nearest even number. Example: 31.5 inches becomes a 32 band.
Step 2: Calculate cup difference
We compare your full bust measurement to your estimated band size. The difference (in inches) maps to a cup letter:
- 1" difference ≈ A cup
- 2" difference ≈ B cup
- 3" difference ≈ C cup
- 4" difference ≈ D cup
- 5" difference ≈ DD/E
- 6" difference ≈ DDD/F
Larger differences continue through additional cup letters. Because cup volume changes with band size, cup letters are always relative to the band.
Tips to get better measurements
Use a soft tape measure
A flexible measuring tape gives the most reliable result. If you do not have one, use a string, then compare its length against a ruler.
Measure in front of a mirror
Make sure the tape stays level around your body. A tilted tape can add or subtract up to a full size.
Keep the tape snug, not crushing
For underbust, you want a firm wrap. For bust, keep the tape comfortably close to your body without compressing tissue.
Understanding sister sizes
If your suggested size feels close but not perfect, try sister sizes:
- Go up one band and down one cup (example: 34D → 36C)
- Go down one band and up one cup (example: 34D → 32DD)
Sister sizes keep cup volume similar while changing band tension, which is useful when a band feels too tight or too loose.
Common signs your bra size is off
- Band rides up in the back
- Straps dig in even after adjustment
- Cups gape or wrinkle
- Spillage over cup edges or underarm area
- Center gore (middle panel) does not sit flat
If you notice one or more of these, try nearby sizes and compare comfort after wearing each for at least 10–15 minutes.
Final note
Your calculator result is your best starting point. Different brands grade sizing differently, and style matters (balconette, plunge, full-coverage, sports). Use the estimate, then fine-tune with fit checks and sister sizes to find what feels secure and comfortable for your body.