Bra size calculator with transparent band methods and size-system comparison
Measure a snug, level underbust and the fullest bust circumference. HitEquals shows its band assumption, cup difference, US/UK/EU starting sizes and nearby sister sizes so the estimate can be tested rather than treated as universal.
Inputs used by this calculator
Bra Size Calculator uses the fields below. The starting values reproduce the page example; replace them with values from the same units and time period before using the result.
| Input | Starting example | Accepted value | How it is used |
|---|---|---|---|
| Measurement unit | Inches | Inches · Centimeters | Selects the unit or conversion path used by Bra Size Calculator. |
| Snug underbust | 31.5 | 20 to 200 | Supplies the snug underbust quantity used by the published equation or result breakdown. |
| Full bust | 36 | 20 to 240 | Supplies the full bust quantity used by the published equation or result breakdown. |
| Band method | Direct — nearest even underbust | Direct — nearest even underbust · Traditional +4/+5 method | Chooses which Bra Size Calculator method or unknown the engine evaluates. |
| Primary sizing system | US | US · UK · EU | Supplies the primary sizing system quantity used by the published equation or result breakdown. |
How to measure
Use a soft tape parallel to the floor. Measure snugly around the rib cage where the band sits, then around the fullest bust without compressing tissue. Record both in the same unit.
Band and cup calculation
Direct mode rounds underbust to a nearby even band. Traditional mode applies the older +4/+5 rule. The rounded difference between bust and calculated band selects a cup step.
direct band=nearest even underbustcup step=round(bust−band)Worked example
With 31.5 inches underbust, direct mode selects band 32. A 36-inch bust leaves roughly four inches and maps to D in the displayed US sequence.
US, UK and EU labels
Cup lettering diverges after D, and EU bands use a different number. The table shows parallel labels generated from the same measurements; a brand chart remains decisive.
Sister sizes
Moving one band up generally moves one cup step down to keep similar nominal cup volume; moving one band down moves one cup step up. Shape and wire geometry can still change fit.
Fit checks matter more than the label
A supportive band stays level, the center and wires sit appropriately for the design, and tissue remains contained without painful pressure. Wacoal's fit guidance emphasizes checking the garment after measuring.
Cup labels by rounded difference
| Difference | US | UK | EU |
|---|---|---|---|
| 1 in | A | A | A |
| 2 in | B | B | B |
| 3 in | C | C | C |
| 4 in | D | D | D |
| 5 in | DD | DD | E |
| 6 in | DDD/G | E | F |
Frequently asked questions
Is the calculated size guaranteed to fit?
No. It is a starting point because brands, styles and breast shape differ.
What is a snug underbust measurement?
It is a level rib-cage measurement taken where the bra band sits, firm without painful compression.
Why are two band methods offered?
Retail fitting guides use different conventions; showing both makes the assumption explicit.
Why do US and UK cups differ?
Their letter sequences diverge after D.
What are sister sizes?
They move band and cup in opposite directions to preserve similar nominal cup volume.
Are centimeters converted exactly?
Yes. The engine uses 1 inch = 2.54 centimeters exactly.
What to keep in mind
Bra sizing is not standardized across all brands. Treat the result as a fitting starting point and check the maker's chart, band stability, cup containment and comfort.
Results are rounded for display in US format, with money in dollars and cents; CSV exports keep full calculation precision. This is a calculation summary, not an official certificate.