Calculator
Formula Used
Classic band: round snug underbust. Add 4 when even. Add 5 when odd.
Modern band: round the snug underbust up to the nearest even band.
Relaxed band: use the modern band and add two inches.
Cup difference: effective bust minus band size.
Cup map: 1 inch A, 2 inches B, 3 inches C, 4 inches D, 5 inches DD/E, and so on.
Sister size: one band down means one cup up. One band up means one cup down.
Example Data Table
| Snug Underbust | Full Bust | Method | Estimated Size | Sister Sizes |
|---|---|---|---|---|
| 32 in | 38 in | Classic Retail | 36B | 34C, 38A |
| 31 in | 37 in | Modern Snug | 32DDD/F | 30G, 34DD/E |
| 34 in | 40 in | Relaxed | 36D | 34DD/E, 38C |
How to Use This Calculator
- Choose inches or centimeters.
- Enter your snug underbust measurement.
- Enter your full bust measurement.
- Add loose, tight, leaning, or high bust values when available.
- Select a band method that matches your comfort preference.
- Press the calculate button.
- Review the recommended size, notes, and sister sizes.
- Use the CSV or PDF button to save the result.
Article: Bra Fit Planning Guide
Why Fit Estimates Help
A bra fit calculator gives a quick starting point before trying styles. It compares your band measurement with your bust measurement. The result suggests a band size, a cup size, and nearby sister sizes. It also explains why comfort can change between brands, fabrics, and cuts.
Measure With Care
Good measuring matters more than any formula. Use a soft tape. Keep it level around the body. Measure the underbust while breathing normally. Measure the fullest bust without pulling the tape tight. A leaning bust value can help when tissue is fuller or softer. Optional loose and tight underbust values add more context.
Understand the Calculation
The calculator uses a retail band method by default. It rounds the snug underbust first. It can then add a classic allowance, use a modern snug band, or apply a relaxed choice. The bust difference decides the cup label. One inch usually equals one cup step. The tool also shows sister sizes. A sister size keeps similar cup volume while changing the band.
Check the Fit
Fit should always be checked on the body. The center gore should rest near the chest. The band should feel firm and level. Straps should guide, not carry everything. Cups should not cut into tissue. They also should not wrinkle deeply. If the band rides up, try a smaller band. If cups overflow, move up a cup.
Use the Result Wisely
This estimator is useful for planning. It is not a final fitting appointment. Different store styles can fit differently. Push up, wireless, balconette, demi, and full coverage cuts behave differently. Stretch lace may feel forgiving. Molded cups may feel less flexible. A result is best used as a starting rack range, not a strict rule.
Compare Nearby Sizes
Use the notes beside the result. They explain measurement gaps, adjustment choices, and confidence level. Compare at least two neighboring sizes when shopping. Try the recommended size, one sister size, and one cup variation. This approach reduces returns and helps you find a comfortable daily fit. Recheck measurements after weight change, pregnancy, surgery, or long training breaks. Elastic also relaxes with wear. Replace stretched bras when the band no longer anchors. Record your best sizes by style. Those notes make future shopping faster and easier. Small daily changes can make the same size feel completely different.
FAQs
Is this an official store calculator?
No. This is an independent estimator for planning. Use it to create a starting size range before comparing store styles.
Which measurement is most important?
The snug underbust and full bust are required. They create the band and cup estimate. Optional measurements improve context.
Why does the classic method add inches?
Some retail fitting methods add allowance to the underbust. This can create a looser band and a different cup result.
What are sister sizes?
Sister sizes keep similar cup volume while changing the band. One band down usually means one cup up.
Why is my modern comparison different?
The modern method keeps the band closer to your underbust. It may produce a smaller band and larger cup label.
Should I use centimeters or inches?
Use the unit your tape shows best. The calculator converts centimeters to inches before estimating the final size.
Can one result fit every bra style?
No. Shape, fabric, cup depth, and stretch affect fit. Try neighboring sizes when possible.
When should I measure again?
Measure again after body changes, weight shifts, pregnancy, surgery, or when your current bras feel different.