Why two measurements?
Band supports weight; cup volume comes from bust minus underbust.
Bra Size Calculator
Measure underbust and bust, then get estimated US, UK, and EU bra sizes.
Underbust and bust
Measure snug underbust and fullest bust. Use the same unit system for both.
About this calculator
How to use Bra Size Calculator, plus the formulas and logic behind the results.
Tool description
Bra sizing pairs a band size (underbust) with a cup letter from bust−underbust difference. Brands vary—treat output as a starting point.
How to use
- Wear a thin unpadded bra or measure bare.
- Pull tape snug on underbust, level on bust.
- Select units and enter both numbers.
- Try the suggested size and adjust up/down a band or cup.
Formulas & reference
US band ≈ even inch rounding of underbustCup index from bust − underbust (inches)EU band often equals underbust cm (approx.)
Fitting tips
- Band should sit level on back
- Cups contain tissue without spill or gap
- Underwire sits on rib cage, not breast
- Scoop and swoop when trying bras on
Calculation logic
Measurements convert to inches, band rounds to even inch size, cup letter maps from inch difference using standard letter progression.
UK/US cups align here; EU labeling varies by brand. Professional fittings beat any online estimate.
Bra Size Calculator FAQ
Common questions about this calculator and how to use the results.
Do sizes run differently by brand?
Yes—always try before buying multiple bras.
Sister sizes?
Going down a band and up a cup (or reverse) can share similar cup volume.
Sports bra sizing?
Some use S/M/L; others use traditional band/cup—check the label.
Pregnancy changes size?
Band and cup often shift; remeasure every trimester.
CM vs inches?
Either works here; both convert internally for cup math.