Bra Cup Size Calculator
Enter your measurements to estimate your bra size. For best results, measure while wearing a non-padded bra and keep the tape level all the way around your body.
How this cup size calculator works
This calculator uses a common sizing method: it estimates your band size from your underbust measurement and your cup size from the difference between your bust and band. The result is an estimate, not a strict rule. Different brands, styles, and fabrics can fit very differently even when the label says the same size.
What you need
- A soft measuring tape
- 2 measurements: underbust and bust
- A relaxed stance and level tape placement
How to measure correctly
1) Underbust measurement
Wrap the tape around your ribcage, directly under your bust. Keep it snug but not painfully tight. Breathe out naturally and record the number.
2) Bust measurement
Measure around the fullest part of your bust. Keep the tape level and comfortably fitted against your body without compressing tissue.
3) Choose unit and system
This page supports both inches and centimeters, with output in US or UK cup lettering. Band numbers are displayed in the inch-based format commonly used in US/UK labels.
Understanding band size vs cup size
A lot of people assume cup letters are absolute. They are not. Cup volume changes with band size. For example, a 34D does not have the same cup volume as a 38D. That is why sister sizes exist (for example, 34D is close in cup volume to 36C and 32DD).
- Band size: how the bra fits around your ribcage
- Cup size: the volume difference between band and bust
- Fit quality: depends on shape, strap placement, underwire design, and fabric stretch
US and UK cup labels are different
US and UK sizing match closely for many smaller cup sizes, but they diverge at larger cups. For example, a US DDD/F may correspond to a UK E or F depending on brand conventions. This calculator gives a practical starting point, then you can fine-tune by trying nearby sizes.
Signs your bra fit may need adjustment
- Band rides up your back (band likely too loose)
- Straps dig in deeply (often band support is insufficient)
- Cup overflow or gaping (cup volume mismatch)
- Center gore does not lie flat (cup shape or size issue)
- Underwire sits on breast tissue (cup too small or wrong wire shape)
Practical fitting tips after you calculate
Try a small size range
Once you get an estimate, try that size plus one sister size up and down. Fit can vary by style: balconette, plunge, full coverage, and sports bras all behave differently.
Adjust for your shape
Two people with identical measurements can prefer different bra sizes due to breast root width, fullness distribution, and torso shape. Measurements are a baseline; comfort and support are the final test.
Re-measure over time
Body composition can change from training, hormones, pregnancy, aging, or weight shifts. Rechecking your measurements every few months can improve comfort dramatically.
Frequently asked questions
Is this calculator exact?
No calculator is exact for every brand. Treat your result as a high-confidence starting point.
What if my result feels wrong?
First check measurement technique. Then test sister sizes and different bra cuts. Often the best fit is one step away from the calculated size.
Why does one brand fit and another doesn’t?
Pattern grading, wire width, cup depth, and materials differ widely. Same label, different fit.
Bottom line
This cup size calculator helps you begin with data, then finish with real-world comfort. If your bras are slipping, pinching, or gaping, a quick re-measure can make a big difference in support and confidence.