Bra Size Calculator
Estimate a starting bra size from your underbust and full-bust measurements, then check nearby sister sizes.
Runs in this browser. No upload by this tool.
Measurements
Use a soft measuring tape and keep it level around your body.
Use this as a starting point, then check the actual fit.
Sizing labels are not universal. US cup names above D vary especially by brand. If the band rides up, cups gap, or tissue spills, try nearby sizes and the brand's own chart.
Keep the estimate
Copy a readable summary or download the same current estimate in a local file.
Creates an editable Word report locally in this browser.
Create a valid estimate to enable local exports.
How Bra Size Calculator works
Use the calculator first. The sections below explain the measurement method, worked examples, sister-size logic, supported range, and why the estimate still needs a real fit check.
How to use the calculator
- Choose inches or centimeters.
- Choose US or UK cup labels.
- Measure snugly around the ribcage directly under the bust and enter the underbust value.
- Measure around the fullest part of the bust without pulling the tape tight and enter the full-bust value.
- Review the estimated starting size, band, cup label, and nearby sister sizes, then confirm against the bra brand's chart and actual fit.
Worked examples
30 in underbust + 35 in bust
With US labels, this tool estimates 30DD/E. With UK labels, the same five-inch difference is labeled 30DD.
34 in underbust + 38 in bust
The four-inch bust-minus-band difference maps to a 34D starting estimate in both supported label sequences.
32 in underbust + 37 in bust
The five-inch difference estimates 32DD/E with US labels or 32DD with UK labels.
Centimeters use the same method
Centimeter measurements are converted with 1 in = 2.54 cm before the band and cup steps are applied.
How sister sizes work
For this calculator, one band step down pairs with one cup-volume step up, while one band step up pairs with one cup-volume step down. The result is an approximate alternative to try, not a guarantee that two bras will fit the same.
| Starting estimate | Band down | Band up | What changes |
|---|---|---|---|
| 30DD/E (US) | 28DDD/F | 32D | Band changes by 2; cup-volume step moves in the opposite direction. |
| 30DD (UK) | 28E | 32D | The same rule uses the selected UK cup-label sequence. |
Frequently asked questions
Is the calculated bra size exact?
No. It is a transparent starting estimate. Brand charts, bra style, fabric, body shape, and fit preferences can change the size that fits best.
How does this calculator estimate band size?
It converts the underbust to inches when needed, rounds to the nearest whole inch, and moves an odd rounded value to the next even band number.
How does this calculator estimate cup size?
It rounds the full bust to the nearest whole inch, subtracts the estimated band, and maps that whole-inch difference to the selected US or UK cup-label sequence.
What does 30 inches underbust and 35 inches bust estimate?
Using this tool's method, the five-inch difference estimates 30DD/E with US labels or 30DD with UK labels.
Can I calculate bra size in centimeters?
Yes. The calculator converts centimeters to inches using 2.54 centimeters per inch, then applies the same documented estimate method.
What are sister sizes?
Sister sizes are nearby band and cup-label combinations intended to approximate similar cup volume. They are useful alternatives to try, not guaranteed equivalents across brands.
Why can my size differ between bra brands?
Bra labels and fit are not universal. Brand charts, cup naming above D, construction, fabric, style, and individual fit preferences can all change which size fits best.
What range does this calculator support?
This implementation supports estimated band sizes 24 through 60 and cup-difference indexes 0 through 15. Values outside that Tool support boundary return an unsupported-range message rather than being forced into a size label.
Which file formats can I save?
A valid estimate can be copied or saved locally as a Word DOCX, Markdown, plain text, JSON, or through the browser Print / Save PDF workflow.
Is an account required?
No account is required to calculate, copy, or download a result with this version of the tool.
Method and limitations
This candidate uses one documented two-measurement estimate. It does not claim that one bra-sizing formula is universal.
Centimeters are converted to inches using 1 in = 2.54 cm.
Underbust is rounded half-up to the nearest whole inch; an odd rounded value moves to the next even band.
Full bust is rounded half-up to the nearest whole inch, then estimated band is subtracted from that rounded full-bust value.
The difference index maps to the selected US or UK cup-label sequence. The supported index is 0 through 15.
Band down 2 pairs with cup index up 1; band up 2 pairs with cup index down 1 when both results remain supported.
The Tool supports estimated bands 24 through 60. This is an implementation boundary, not a universal physical or retail limit.
Use the result as a starting point. Confirm the bra brand's size chart and actual fit. This tool does not guarantee garment fit or replace an in-person fitting.
Runs in this browser. No upload by this tool. Copy and download locally, then review before sharing.