Bra Size Calculator
Use our free bra size calculator to find your perfect band size and cup size from simple underbust and bust tape measurements. This bra fitting calculator translates your measurements in inches or centimeters to US or UK sizing standards and shows your closest sister sizes for alternative fits. Whether you need to measure bra size at home or want an accurate bra size recommendation, this tool provides reliable results with a clear measurement guide.
How to Use the Bra Size Calculator
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Mathematical Formula & Logic
Step-by-Step Worked Calculation
Scenario: Determining US Sizing
A person has a snug underbust measurement of 31.5 inches and a full bust measurement of 36 inches.
Step 1: Calculate band size. Underbust 31.5 is rounded to the nearest even number: 32.
Step 2: Subtract band size from full bust: 36 - 32 = 4 inches.
Step 3: Translate 4-inch difference to cup letter: 1" = A, 2" = B, 3" = C, 4" = D.
Step 4: Output recommended size: 32D.
How to Use the Bra Size Calculator
- 1. Step 1: Measure your underbust (directly beneath the breasts) snugly with a tape measure for the bra size calculator.
- 2. Step 2: Measure your full bust (across the fullest part of the breasts) loosely for the band and cup calculation.
- 3. Step 3: Select your preferred sizing system (US or UK) to see your bra size in the correct standard.
- 4. Step 4: Review your recommended band size (number) and cup size (letter) from the bra calculator.
- 5. Step 5: Check your closest sister sizes — alternative band/cup combinations with the same cup volume.
- 6. Step 6: Use the measurement tips to verify your tape placement for the most accurate bra size result.
- 7. Step 7: Compare your bra size result against common fitting issues to ensure optimal comfort and support.
What Is a Bra Size Calculator?
Bra size consists of two components: the band size (a number like 32, 34, 36) derived from the underbust measurement, and the cup size (a letter like A, B, C, D) determined by the difference between the bust and band measurements. Sister sizes are alternative bra sizes that share the same cup volume but have different band lengths, providing fit flexibility across different manufacturers.
Why This Calculation Matters
Wearing the correct bra size is essential for comfort, support, and long-term breast health. Studies show that up to 80% of women wear the wrong bra size, leading to back pain, shoulder strain, poor posture, and premature wear of bras. An accurate bra size calculation helps women find properly fitting bras that provide adequate support without discomfort.
Common Mistakes to Avoid
- Measuring the bust too tightly — the bust measurement should be taken loosely across the fullest part of the breasts without compressing tissue. A tight measurement produces an undersized cup recommendation.
- Rounding the band size to the nearest even number incorrectly — some measurement methods add 4 or 5 inches to the underbust for US sizing, while others round to the nearest even number. Our calculator handles this conversion automatically.
- Ignoring sister sizes when trying new bras — if a bra fits well in the cup but the band feels tight, try the sister size with a larger band and one cup smaller. Sister sizes maintain the same cup volume for better fit flexibility.
- Not remeasuring after weight changes or pregnancy — bra size can change significantly with weight fluctuations, pregnancy, breastfeeding, and aging. Remeasure every 6-12 months or after any notable body changes.
Frequently Asked Questions
Complete indexable directory of answers (127 questions)
What is a bra size calculator?
A bra size calculator determines your correct bra size based on band and bust measurements.
What is band size?
The measurement around your ribcage under your bust, rounded to the nearest even number.
What is bust size?
The measurement around the fullest part of your bust.
What is cup size?
Determined by the difference between bust and band measurements.
What is bra size?
The combination of band size and cup size (e.g., 34C).
What is proper band fit?
Band should be snug, level, and parallel around the body.
What is proper cup fit?
Cup should fully contain breast tissue without gapping or spilling.
What is sister size?
Different bra size with same cup volume.
What is US sizing?
American bra sizing system with letters AA through K+.
What is UK sizing?
British sizing system with different lettering for larger cups.
What is EU sizing?
European sizing using B, C, D, E, F, G, etc.
What is bra sizing variation?
Different brands may size slightly differently.
What is professional fitting?
Expert measurement for accurate sizing.
What is bra calculator accuracy?
Calculator provides estimate; professional fitting is most accurate.
What is bra sizing importance?
Correct size ensures comfort, support, and health.
How do I calculate my bra size?
Enter band and bust measurements. Calculator shows size.
How do I use this calculator?
Input measurements. Click "Calculate" for bra size.
How do I measure band size?
Measure under bust, round to nearest even number.
How do I measure bust size?
Measure around fullest part, parallel to floor.
How do I calculate cup size?
Subtract band from bust measurement.
How do I calculate for US sizing?
Use US cup size chart.
How do I calculate for UK sizing?
Use UK cup size chart.
How do I calculate for EU sizing?
Use European conversion.
How do I find sister size?
Calculator shows equivalent sizes.
How do I calculate for different brands?
Note brand variations.
How do I calculate for different body types?
Use standard calculation.
How do I calculate for athletic build?
May need different size.
How do I calculate for plus sizes?
Extended size ranges available.
How do I calculate for petite?
Petite band sizes.
How do I calculate for nursing?
Size may change during nursing.
How do I calculate for sports bras?
Different sizing considerations.
How do I calculate for wireless bras?
Same sizing method.
How do I calculate for strapless bras?
Same sizing, different fit.
How do I calculate for bikini tops?
Some use bra sizing.
How do I calculate for education?
Learn about bra fitting.
Why proper bra size matters?
Correct size provides support, comfort, and prevents health issues.
Why most women wear wrong size?
Studies show 80% wear incorrect size.
Why cup size calculation matters?
Wrong cup causes discomfort.
Why band size matters?
Band provides 80% of support.
Why sister sizes matter?
Different sizes can fit similarly.
Why sizing varies by brand?
Different standards used.
Why measurement technique matters?
Proper technique ensures accuracy.
Why age affects size?
Body changes with age.
Why weight changes affect size?
Weight affects measurements.
Why proper fit affects health?
Ill-fitting bras cause pain.
Can I calculate for any band size?
Yes. Any band measurement.
Can I calculate for any cup size?
Yes. AA through large cups.
Can I calculate for US sizing?
Yes. Standard US sizes.
Can I calculate for UK sizing?
Yes. UK conversion.
Can I calculate for EU sizing?
Yes. European conversion.
Can I calculate sister sizes?
Yes. Equivalent sizes shown.
Can I calculate for different brands?
Yes. Note variations.
Can I calculate for plus sizes?
Yes. Extended ranges.
Can I calculate for petite?
Yes. Petite sizes.
Can I calculate for different body types?
Yes. Standard calculation.
Can I calculate for nursing bras?
Yes. Size may change.
Can I calculate for sports bras?
Yes. Different considerations.
Can I calculate for different styles?
Yes. Same method.
Can I calculate for education?
Yes. Learn about sizing.
Can I calculate for shopping?
Yes. Purchase guide.
Is this calculator accurate?
Yes. Standard formulas used.
Is this calculator free to use?
Yes. No registration.
Is this calculator private?
Yes. Browser calculations.
Is this calculator reliable?
Yes. Standard methods.
Is this calculator suitable for shopping?
Yes. Helps decisions.
Is this calculator maintained?
Yes. Updated regularly.
Is this calculator mobile-friendly?
Yes. All devices.
Is this calculator better than guessing?
Yes. Calculated vs guesswork.
Is this calculator suitable for individuals?
Yes. Personal sizing.
Is this calculator a substitute for fitting?
No. Professional most accurate.
What is the difference between US and UK sizing?
Different lettering for larger cups.
What is the difference between band and cup?
Band is ribcage. Cup is difference.
What is the difference between sister sizes?
Same cup volume, different combination.
What is the difference between calculator and tape?
Calculator computes. Tape measures.
What is the difference between bra and clothing size?
Different systems.
What is the difference between exact and approximate?
Exact uses measurements.
What is the difference between bra and sports bra?
Different fit expectations.
What is the difference between wireless and underwire?
Same sizing, different comfort.
What is the difference between full coverage and demi?
Same size, different coverage.
What is the difference between size and volume?
Size is combination. Volume is capacity.
When should I calculate bra size?
When purchasing new bras.
When should I remeasure?
After weight changes or annually.
When is sizing important for shopping?
Before purchasing.
When is sizing important for comfort?
When experiencing discomfort.
When is sizing important for health?
When experiencing pain.
When is sizing important for styles?
Different styles may require adjustments.
When is sizing important for exercise?
Sports bras need support.
When is sizing important for occasions?
Formal wear may differ.
When is sizing important for pregnancy?
Size changes during pregnancy.
When is sizing important for education?
When learning about fit.
Does this calculator show bra size?
Yes. Calculated size.
Does this calculator show sister sizes?
Yes. Equivalent sizes.
Does this calculator handle multiple systems?
Yes. US, UK, EU.
Does this calculator work offline?
Yes. Local calculations.
Does this calculator show size chart?
Yes. Cup size chart.
Does this calculator save results?
No. Privacy protected.
Does this calculator show measurement tips?
Yes. Guidance provided.
Does this calculator handle extended sizes?
Yes. AA through large.
Does this calculator show brand variations?
Yes. Differences noted.
Does this calculator work on all browsers?
Yes. All modern browsers.
Which sizing system should I use?
Use system in your region.
Which measurement is most important?
Both equally important.
Which feature is most important?
Accurate calculation and sister sizes.
When should I use sister size?
When standard unavailable.
How do I know if correct?
Band parallel, cups contain, straps comfortable.
How do I calculate for 32 band, 34 bust?
Difference = 2". Cup = B. Size = 32B.
How do I calculate for 36 band, 40 bust?
Difference = 4". Cup = D. Size = 36D.
How do I calculate sister size for 36C?
Sister sizes: 34D, 38B.
How do I calculate for sports bra?
May prefer tighter band.
How do I calculate for nursing bra?
Measure when fullest.
How do I convert US to UK?
Use conversion chart.
How do I measure correctly?
Under bust and fullest part.
How do I know if cup too small?
Spilling or discomfort.
How do I know if band too loose?
Rides up in back.
What is the cup formula?
Cup = Bust - Band
What is US cup chart?
0"=AA, 1"=A, 2"=B, 3"=C, 4"=D, 5"=DD, 6"=DDD
What is band rounding?
Nearest even number.
What is sister size formula?
Up band, down cup (or vice versa).
What is proper fit?
Band parallel, cups smooth, straps comfortable.
Why can't enter invalid values?
Must be positive.
Why different from store?
Brands vary.
Why doesn't fit after calculating?
Try sister size.
Why measurements vary?
Same conditions needed.
Why professional fitting?
Most accurate method.
How does the Bra Size Calculator calculate its results?
The Bra Size Calculator uses verified mathematical formulas processed entirely in your browser. Calculator inputs and results are never sent to external servers. We do use Google Analytics and AdSense for standard website operation — see our Privacy Policy for details.
Is my data safe when using this Bra Size Calculator?
Yes. All calculations happen locally in your browser. We never store, transmit, or log any input data you enter into the calculator.
What should I do if I get an unexpected result?
Double-check that all inputs are valid numbers within reasonable ranges. If you believe there is an error, please contact us with your input values and we will investigate.