1. Measure Underbust
Wrap the tape around your ribcage directly under the bust. Keep it snug and level around your body.
Calculator
Bra Size Calculator: Find Your Band & Cup Size
Use this bra size calculator to find a measurement-based starting size. Measure snugly under your bust and around the fullest part of your bust, enter both numbers in inches or centimetres, and the calculator estimates your band and cup size.
Choose the sizing system you shop in: United States, United Kingdom, Europe, France / Spain / Belgium or Australia / New Zealand. Your primary result uses the selected system, with additional regional labels shown from the same measurements. Fit varies by brand and style, so treat the result as a starting point.
Trust and methodology
How This Calculator Is Reviewed
- Calculation type
- Measurement-based sizing estimate
- Jurisdiction
- US, UK, EU, FR, and AU/NZ sizing labels
- Last reviewed
- 2026-07-22
Use the result as a starting size to try, not as a promised fit.
Primary Sources
- Measurement-based band and cup-label calculation rulesProCalculator methodologyThe calculator uses a measurement-based sizing method rather than a medical or brand-specific standard.
Known Limitations
- Brand-specific fit differences are not modeled.
- Body shape, style, fabric, wire shape, and personal comfort preferences can change fit.
- This is not medical advice and does not diagnose fit, pain, posture, or health concerns.
Found a calculation issue, outdated source, accessibility problem, or unclear assumption? Contact us.
Enter Your Measurements
Choose the sizing system you normally shop in, then enter your underbust and bust measurements.
Measurement guide
How to Measure for Bra Size
2. Measure Fullest Bust
Measure around the fullest part of the bust. The tape should sit flat without pressing into the body.
3. Keep the Tape Level
Check that the tape is not dipping in the back or angled across the front.
4. Avoid Overtightening
A tight tape can change the result. Aim for contact with the body, not compression.
5. Enter Both Measurements
Use the same unit for both fields, or switch units before calculating. Decimal measurements are supported.
A snug underbust measurement and an uncompressed bust measurement help provide a consistent starting point; repeat each measurement if the tape slips or tilts.
Methodology
How the Calculator Works
The calculator uses underbust and bust measurements as inputs. It normalizes the measurements, estimates a starting band from the underbust value, compares the bust measurement with that band, and applies the selected regional sizing label.
This is a deterministic measurement method for a starting size. It does not replace a brand's own fit guidance, and bra sizing is not perfectly standardized across every manufacturer.
Measurement relationship
Cup label is based on the difference between bust measurement and the estimated band reference. Band and cup labels are then mapped to the selected regional sizing system.
International Sizing Information
Equivalent starting sizes can use different labels across regions. For example, the same measurements that estimate US 32D may display as UK 32D, EU 70D, FR 85D, or AU/NZ 10D.
These labels are regional conventions. Some brands may still vary, especially at larger cup sizes or in specialized styles.
Understanding Your Result
Band
The number portion describes the estimated band label. It is based on the ribcage measurement under the bust.
Cup
The letter portion describes the bust-to-band difference. Cup letters are relative to band size, so 32D and 36D do not represent the same cup volume.
Starting Size
Treat the result as the first size to try. If a band rides up, cups gape, or cups spill, nearby sizes or different styles may fit better.
Fit Guidance
- The band should feel secure without excessive discomfort.
- Cups should not noticeably spill, wrinkle, or gape.
- Straps should help stabilize the bra without carrying all support.
- Center fit can vary by style, wire shape, and body shape.
Bra Size Calculator FAQ
How accurate is a bra size calculator?
It can estimate a useful starting size from body measurements, but fit still varies by brand, style, fabric, and body shape. Use the result as a first size to try, not as a promised fit.
Should I measure in inches or centimeters?
Use whichever unit is easiest for you. The calculator normalizes measurements internally, so equivalent inch and centimeter measurements are intended to produce the same starting size.
Why does my bra size differ between brands?
Bra sizing labels are regional conventions, and brands can cut bands, wires, and cup shapes differently. A measured size is a starting point, while each brand's fit notes and size chart can still matter.
What if I am between sizes?
Remeasure once to confirm the numbers, then use comfort and the brand's size chart to decide which nearby size to try first. Small differences in fabric and style can change the best choice.
Are US and UK cup sizes the same?
They match through some smaller cup labels, but the progressions diverge around DD and above. Select the sizing system you normally shop in before calculating.
How often should I remeasure?
Remeasure when your current bras stop fitting well or after changes that can affect measurements, such as weight change, pregnancy, surgery, or major changes in activity.
What are sister sizes?
Sister sizes are sizes with similar cup volume on a different band, for example 32D, 34C and 30DD. If the band of your calculated size feels too tight or loose, a sister size can be a useful next try. This calculator does not calculate sister sizes. It shows your measurement-based starting size and regional labels from the same measurements.
Can I convert my size between US and UK sizing?
Yes. Choose the sizing system you shop in before you calculate. Your primary result uses that system, with additional regional labels shown from the same measurements. Band numbers are usually the same in US and UK sizing, but larger cup letters can differ, so check the brand's own chart as well.
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This calculator provides a measurement-based starting size. Actual fit may vary by brand, style, shape, construction, and personal preference. For difficult fit issues, compare with the brand's size chart or consult a professional fitter. It is not medical advice. Read the full disclaimer.