Formula Used
Unit conversion: inches = centimeters ÷ 2.54.
Modern band: band = nearest even number to adjusted underbust.
Traditional band: band = rounded underbust plus four or five.
Cup difference: cup difference = full bust − band reference.
Cup step: about one inch difference adds one cup level.
Sister sizes: one band down uses one cup up. One band up uses one cup down.
How To Use This Calculator
- Measure high bust above the fullest chest area.
- Measure full bust around the fullest point.
- Measure underbust where the band rests.
- Select inches or centimeters.
- Choose your sizing system and band method.
- Press calculate to view the result above the form.
- Use CSV or PDF export for your records.
Example Data Table
| High Bust |
Full Bust |
Underbust |
Unit |
System |
Estimated Result |
| 34 |
38 |
32 |
in |
US |
32DDD/F |
| 86 |
94 |
75 |
cm |
EU |
75E |
| 36 |
40 |
34 |
in |
UK |
34DD |
Understanding Three Measurement Bra Sizing
A three measurement method looks at high bust, full bust, and underbust. It gives a broader view than one tape reading. The high bust shows the upper chest frame. The full bust shows the largest chest circumference. The underbust shows the rib cage where the band sits.
Why This Method Helps
Bra fit depends on both support and volume. The band carries most support. The cup holds breast volume. When the band is loose, straps often dig in. When the cup is small, tissue may spill over. Three measurements help detect these issues before buying.
The calculator first standardizes units. It can read inches or centimeters. Then it rounds the underbust using the chosen band method. The modern method uses the nearest even band. The traditional method adds fitting ease. A relaxed setting allows more room. A firm setting gives a snugger band.
Cup volume comes from the bust difference. This is the full bust minus the band reference. Each inch usually adds one cup step. A one inch difference is often an A cup. Two inches often means B. Three inches often means C. Larger differences continue through the cup scale.
Using The Result
Treat the result as a starting point. Different brands use different shapes. Fabric stretch also changes the feel. A molded cup may fit tighter. A stretch lace cup may feel softer. The same size can feel different across styles.
High bust data adds another check. A large gap between high bust and full bust may show projected shape. A small gap may show shallow shape. These notes help when choosing cup style. They also help when comparing sister sizes.
A good fit feels stable. The band should stay level. The center gore should sit close. Cups should hold tissue without gaps or overflow. Straps should guide the cup, not carry all weight.
Measure again after weight change, pregnancy, surgery, or exercise changes. Also measure when old bras feel loose or painful. Use the exported record to compare future fittings. It also documents changes for later style planning. This reduces guesswork during online ordering. A measured estimate cannot replace a fitting room check, but it makes shopping more focused and confident.
FAQs
What are the three measurements?
They are high bust, full bust, and underbust. Together, they estimate frame size, cup volume, and breast shape more clearly than one measurement.
Which measurement controls the band?
The underbust measurement controls the band. It shows the rib cage size where the bra band should sit and provide support.
Which measurement controls the cup?
The full bust measurement helps control cup volume. The calculator compares it with the band reference to estimate the cup letter.
Why use high bust measurement?
High bust measurement adds shape context. It can show whether the bust is shallow, balanced, or projected compared with the full bust reading.
Are sister sizes exact matches?
No. Sister sizes are nearby options. They keep similar cup volume but change band feel. Try them when the band feels too tight or loose.
Why do brands fit differently?
Brands use different patterns, fabrics, wires, and cup depths. The same label can feel different across balconette, plunge, molded, or stretch styles.
Should I round my measurements?
Use the rounding option that matches your tape accuracy. Quarter inch rounding works well for careful measurements. Whole inch rounding is faster.
Is this result final?
No. It is a strong starting point. Always check comfort, band position, cup smoothness, strap pressure, and movement before choosing a final size.