bra cup size calculator in cm

How this bra cup size calculator in cm works

This calculator uses a simple and practical method: it compares your full bust measurement to your snug underbust measurement. The difference between those two values in centimeters gives an estimated cup depth. Your underbust measurement is then rounded to common band sizing steps.

The result gives you a starting point, not an absolute rule. Bra sizing can vary by brand, style, and fabric stretch, so always treat the output as a fitting guide.

Quick formula

• Cup difference (cm) = Full bust (cm) - Underbust (cm)
• Estimated EU band = Underbust rounded to nearest 5 cm
• Estimated UK band = Underbust converted to inches and rounded to nearest even number

How to measure accurately

1) Measure your underbust

Wrap the tape directly under your bust, parallel to the floor. Breathe out gently and keep the tape snug. Record this number in cm.

2) Measure your full bust

Wrap the tape around the fullest part of your bust. Keep your arms relaxed, tape level, and avoid squeezing the tissue. Record this number in cm.

3) Enter both numbers

Put those values into the calculator above and click Calculate Size. You’ll see your estimated cup difference and sizing suggestions.

Approximate cup progression in centimeters

The calculator follows an approximate cup scale like this:

• Under 10 cm difference: AA
• 10 to 11.9 cm: A
• 12 to 13.9 cm: B
• 14 to 15.9 cm: C
• 16 to 17.9 cm: D
• 18 to 19.9 cm: E (or DD in UK labels)
• 20 to 21.9 cm: F (or E in UK labels)
• 22 cm and above: progressively larger cup letters

Different manufacturers use slightly different grading, especially in higher cup ranges. That’s why trying sister sizes is often helpful.

What are sister sizes?

Sister sizes keep roughly the same cup volume while changing band tightness. If one band feels too tight, go up one band and down one cup. If a band feels too loose, go down one band and up one cup.

• Example: 75C is close in cup volume to 80B and 70D
• Use this when the cups fit but the band does not

Common fitting checks after calculating

• Band: should feel snug and level around your torso.
• Cups: no overflow at top/sides and no empty wrinkling.
• Center gore: should sit close to your sternum (for wired bras).
• Straps: supportive but not digging into shoulders.

FAQ

Is this calculator accurate for everyone?

It’s accurate as a starting estimate for many people, but body shape and brand differences matter. Final fit should always be checked physically.

Why do I get a different size in another brand?

Brands use different patterns, cup scaling, and stretch materials. Even within one brand, balcony, plunge, and sports bras can fit differently.

Can I use this during weight changes or hormonal changes?

Yes. Re-measure every few months if your body changes. Small changes in tissue and ribcage measurement can alter your best fit.

Final note

A good bra size should feel secure, balanced, and comfortable through a full day of movement. Use this bra cup size calculator in cm to get your baseline, then fine-tune by trying nearby sizes and styles.