What are sister sizes?

Sister sizes are bra sizes with the same cup volume but a different band size (for example, 34C ↔ 32D ↔ 36B). They can help you fine-tune band tightness while keeping a similar cup fit.

Why do US and UK cup sizes differ?

US and UK sizing systems use different cup lettering progressions. This calculator provides both so you can shop in either sizing system.

Why might my calculated size feel off?

Bra sizing varies by brand, style, and personal preference. Recheck measurements, ensure the tape is level, and try sister sizes if you’re between sizes.

Bra Size Calculator

Overview

Enter your underbust and bust measurements to estimate your bra band and cup size, plus sister sizes.

Measure your underbust (snug, just under the bust) and your bust at the fullest part. This calculator estimates your US and UK bra size and provides sister sizes to help fine-tune fit.

How to use

Estimate your bra size in a few quick steps.

Measure your underbust: Measure snugly around your ribcage, just under your bust. Keep the tape level and parallel to the floor.
Measure your bust: Measure around the fullest part of your bust, again keeping the tape level.
Enter your measurements: Enter both measurements and select the correct units.
Review your size and sister sizes: Use the recommended band and cup size as a starting point, then check sister sizes if you’re between sizes or want a tighter/looser band.

FAQs

What are sister sizes?: Sister sizes are bra sizes with the same cup volume but a different band size (for example, 34C ↔ 32D ↔ 36B). They can help you fine-tune band tightness while keeping a similar cup fit.
Why do US and UK cup sizes differ?: US and UK sizing systems use different cup lettering progressions. This calculator provides both so you can shop in either sizing system.
Why might my calculated size feel off?: Bra sizing varies by brand, style, and personal preference. Recheck measurements, ensure the tape is level, and try sister sizes if you’re between sizes.