Bra Size Calculator
Adjust the inputs below. Results update as you type.
How it works
Band size = measurement around the ribcage just under the bust, rounded to nearest even number. Cup size = bust measurement minus band measurement: 1 inch = A, 2 = B, 3 = C, 4 = D, etc. Sizing varies by brand—always try before buying. Sister sizes (same cup volume, different band) can help when your size isn't available.
Input guidance
- Confirm date/time/unit settings before comparing outputs.
- If a task has optional fields, run both with and without them to understand impact.
- Save scenario variants when making practical decisions.
The formula
Band size comes from the underbust measurement; cup size from the difference between bust and underbust (about 1 inch per cup).
Worked example
An underbust of 32 inches and bust of 35 inches gives a 3-inch difference, roughly a 32C in US sizing.
More examples to test
- Quick-pass example: run default assumptions for a first estimate.
- Refined example: update one assumption at a time to isolate impact.
How to interpret results
Use outputs as operational estimates and pair them with local constraints, business rules, or provider requirements.
When this can be inaccurate
Utilities can miss local policy details, special-case rules, and environment-specific constraints.
Change history
- July 2026: Quality-reviewed for publication with formula checks and explanatory copy updates.
Site-wide corrections also appear on the corrections log.
Find productivity tools for everyday workflows
General recommendation, not professional advice.
Frequently asked questions
How do I measure for a bra?+
Measure snugly around your ribcage under the bust for the band, and around the fullest part of the bust for the cup difference.
Why do sizes feel inconsistent?+
Sizing varies by brand and country, and band and cup are linked (sister sizes), so the same body may fit several labeled sizes.
What are sister sizes?+
Sizes with the same cup volume but different bands, like 34B and 32C. If a band feels off, a sister size may fit better.
Why are outputs slightly different from another tool?+
Different tools can use different rounding rules, default assumptions, and treatment of edge cases.
How can I improve estimate reliability?+
Use verified inputs from real records and re-run calculations after major assumption changes.