Bra Band Size Calculator
Use our free bra size calculator to find your perfect fit. Enter your measurements and get instant results in US, UK, EU, and 7+ international sizing systems.
Your data is never stored or shared. All calculations happen in your browser.
Enter your measurements to see your bra size results here
Results include US, UK, EU, FR, IT, AU, and JP sizes
Why Band Size Matters More Than Most Shoppers Think
The band is the foundation of bra support. It wraps the ribcage and anchors the cups; straps should only fine-tune lift. When the band is wrong, cups rarely fit correctly even if the letter looks right on paper. Our band-focused calculator isolates underbust measurement to help you verify whether band issues—not cup size—are driving discomfort.
Many women report wearing bands that ride up in back. Industry estimates often suggest that tightening hook settings or choosing a smaller band with larger cup (sister size) resolves strap pain and cup gaping more often than changing cup alone.
How to Measure Your Band (Underbust) Accurately
- Stand upright with feet hip-width apart.
- Place the tape directly under the breast tissue, parallel to the floor.
- Pull the tape snug—firm contact without indenting skin.
- Measure at the end of a normal exhale.
- Check front and back in a mirror; the tape should not slope.
Record inches or centimeters consistently. Round to the nearest half unit before using the calculator.
From Raw Underbust to Labeled Band Size
US sizing often adds inches to the measured underbust to produce even band numbers (32, 34, 36). UK sizing frequently uses the measured underbust in inches as the band label. EU sizing maps centimeters to standardized steps. These rules explain why the same body may wear 34 in one system and 75 in another. Our calculator converts among systems once you enter your measurement.
Signs Your Band Is Too Large
- Back band climbs toward shoulder blades during the day
- Straps slip even when adjusted short
- You fasten the tightest hook on a new bra and still feel loose
- Cups seem to “float” or gap despite smaller cup trials
Try one band size down and one cup size up. Example: if 36C feels loose in band with gaping cups, test 34D.
Signs Your Band Is Too Small
- Painful digging along the ribcage
- Skin bulge above or below the band line (sometimes called “back fat” but often a band fit issue)
- Difficulty fastening without stretching the hook excessively
- Center gore tilts away from the body
Try one band up and one cup down, or a bra with a taller wing for broader back coverage without changing volume.
Hook Placement and Band Longevity
New bras should fit on the loosest hook, allowing you to tighten as elastic relaxes over weeks and months. If you begin on the middle hook, you have little room to compensate for stretch. Replace bras when the loosest hook feels like the old tightest hook.
Band Size vs Sister Size
Changing band while adjusting cup keeps similar breast volume. This is essential when a brand’s band runs large or small. Use our sister size calculator alongside band results.
Special Considerations
Soft tissue and compressibility
Some bodies compress more under a firm band; others need firmer bands to prevent ride-up. Personal preference within fit guidelines is valid.
Long torso vs short torso
Band height affects comfort at the underarm; a short wing may dig even when the labeled band is correct.
When to Remeasure Band Size
- Weight change affecting ribcage
- Pregnancy or postpartum rib expansion
- Switching from wired to wireless styles that fit differently
- Age-related changes in torso shape
Brand Variance Disclaimer
“True to size” bands differ by brand elasticity and fabric. Sports bras and bralettes may use alpha sizing derived from band ranges—always cross-check brand charts. Pair band calculator output with full bra size calculator results for cup pairing.
Measuring Band With Different Body Types
Athletic builds with muscular backs may prefer slightly firmer bands to prevent shift during activity. Softer tissue around the ribcage may show temporary skin above or below the band line when the band is actually correct—distinguish tissue redistribution from a too-tight band by checking whether the band stays level and hooks comfortably. Long-waisted torsos sometimes need bras with taller sides; short-waisted shoppers may prefer lower wings even when band number is correct.
Documenting Band Fit Over Time
Photograph the back band level in a mirror when a bra fits well. When fit drifts months later, compare photos before buying a new size—elastic loss mimics cup problems. Note which hook row you use on each bra; migrating to tighter hooks across your drawer signals it is time to remeasure.