Estimate your band and cup size from your underbust and bust measurements.
Understanding the bra size calculation
Enter your underbust (band) and fullest bust measurements and this calculator estimates a US band and cup size from the difference between them.
Fit varies by brand and style, so treat it as a starting point.
Worked example
On the values this calculator opens with, the size is 32D. Underneath, Band size comes out at 32 and Cup at D. Change any field and every figure updates as you type.
Using the calculator
- Choose inches or centimetres.
- Measure your underbust and fullest bust.
- Read the estimated band and cup.
The calculation
band ≈ rounded underbust measurement
cup ≈ bust − band (each inch = one cup up)
Frequently asked questions
How do I measure for a bra?
Measure snugly around your ribcage under the bust for the band, and around the fullest part for the bust. The difference sets the cup.
Why do sizes vary by brand?
Cut, materials and sizing standards differ between makers, so the same label fits differently. Use this as a guide.
What if I’m between sizes?
Try the nearer band and adjust the cup, or test both — fit preference and style matter as much as the numbers.