Bra Size Calculator
Enter your underbust and bust measurements to estimate your best starting bra size.
Tip: This tool gives a strong starting point. Final fit can vary by brand, style, and cup shape.
How this perfect bra size calculator works
A bra size has two parts: the band size and the cup size. The band is based on your ribcage (underbust), and the cup is based on the difference between your bust and band measurements.
This calculator uses a practical modern fitting method:
- Band size: nearest even number to your snug underbust in inches.
- Cup size: based on the difference between bust and calculated band.
- Regional conversions: includes UK/US estimate plus EU band equivalent.
How to measure correctly
1) Underbust measurement
Wrap a soft measuring tape around your ribcage, directly under your bust. Keep the tape level and snug (not painfully tight). Exhale naturally before reading the number.
2) Bust measurement
Measure around the fullest part of your bust while standing naturally. Keep the tape level across your back and avoid compressing breast tissue.
3) Double-check your numbers
Take each measurement two or three times. Small errors (even half an inch) can shift your suggested cup size.
Understanding your result
If your result says 34D, that means:
- 34 = approximate band size.
- D = cup volume relative to that band.
Cup letters are not absolute. A 34D does not have the same cup volume as a 38D. Cup volume scales with band size.
Sister sizes (very useful)
If your recommended size feels close but not perfect, try sister sizes:
- Go up one band size and down one cup size (example: 34D → 36C).
- Go down one band size and up one cup size (example: 34D → 32DD).
Sister sizes keep cup volume similar while changing band tension.
Common fit problems and fixes
Band rides up in back
The band may be too loose. Try one band size down and one cup size up.
Straps digging in
Straps should not carry most of the support. Usually this means the band is too loose or cups are wrong.
Spillage at top or sides
Cups are likely too small (or wrong shape). Try a larger cup size first.
Wrinkling or empty cup space
Cups may be too large, or the bra shape may not match your natural shape. Try one cup down or a different style.
Quick fit checklist
- Band feels firm and level around your torso.
- Center gore sits comfortably against your chest (for wired bras).
- Underwire, if present, surrounds tissue without sitting on it.
- Straps stay in place without digging.
- You can move naturally without shifting or discomfort.
FAQ
Is this calculator accurate?
It is accurate as a starting size estimate. Final fit depends on brand sizing, cup shape, and bra style.
Why do I get different sizes in different brands?
Brand grading and fabric stretch vary. A perfect fit in one line may require a different size in another.
How often should I remeasure?
Every 6–12 months, or after body changes like weight fluctuation, hormonal changes, pregnancy, or training changes.
Final thoughts
The best bra size is the one that supports you comfortably all day. Use the calculator result as your baseline, then fine-tune with sister sizes and style adjustments. Fit should feel secure, balanced, and natural.