Bra Size Calculator in Inches | Find Your Perfect Fit

  • Adam
  • November 12, 2025

Free bra size calculator in inches. Calculate your band and cup size with accurate US measurements. Step-by-step guide, size charts & sister sizes included.

Bra Size Calculator in Inches – Find Your Perfect Fit (US Sizing)

The bra size calculator in inches helps you determine your correct bra size using US measurements for accurate, comfortable fit. Whether you're shopping for your first bra, experiencing fit issues, or simply want to confirm your size, this calculator uses your underbust and bust measurements in inches to calculate both band size and cup size according to standard US bra sizing methods.

📏 Calculate Your Bra Size

Enter your measurements to find your perfect fit

Measure snugly under your bust
Measure around fullest part of bust

Your Bra Size

Recommended Size (US)
34C
Band Size
34
Cup Size
C
Cup Difference
3"

Sister Sizes (Alternative Fits)

These sizes have the same cup volume but different band lengths:

Important Fit Tips:

  • The band should be level around your body, not riding up your back
  • You should be able to fit two fingers under the band comfortably
  • The cups should fully contain your breasts without spillage or gaping
  • The center gore (between cups) should lay flat against your sternum
  • Try sister sizes if your calculated size doesn't fit perfectly

How to Measure Your Bra Size in Inches

Accurate measurements are essential for finding the right bra size. Follow these steps carefully for the best results:

What You'll Need

  • Measuring Tape: Use a soft, flexible fabric measuring tape (not a metal one)
  • Mirror: A full-length or large mirror helps ensure the tape is level
  • Minimal Clothing: Measure wearing no bra or a non-padded bra for accuracy
  • Assistance (Optional): Having someone help can make measuring easier and more accurate

Step 1: Measure Your Underbust (Band Size)

📐 Underbust Measurement Instructions

  • Stand upright with your arms at your sides
  • Wrap the measuring tape around your ribcage directly underneath your breasts
  • Keep the tape level and parallel to the floor all the way around your body
  • Pull the tape snug but not tight—you should be able to breathe comfortably
  • Take the measurement at the end of an exhale for consistency
  • Round to the nearest whole number or half inch

Note: If your measurement is an odd number (like 31 inches), round up to the next even number (32 inches) for your band size.

Step 2: Measure Your Bust (Cup Size)

📐 Bust Measurement Instructions

  • Stand upright with your arms relaxed at your sides
  • Wrap the measuring tape around the fullest part of your bust (usually across the nipples)
  • Keep the tape level and parallel to the floor, not angled downward
  • The tape should be comfortably snug but not compressing your breasts
  • Don't hold your breath—breathe normally while measuring
  • Record the measurement to the nearest quarter inch for accuracy

Bra Size Calculation Formula

Understanding how bra sizes are calculated helps you verify results and make adjustments:

Band Size Formula (US Method)

Standard Method:

Band Size = Underbust Measurement (rounded to nearest even number)

If measurement is odd: Round up to next even number

Example: Underbust = 31 inches → Band Size = 32

Cup Size Formula

Calculate Cup Difference:

Cup Difference = Bust Measurement - Band Size

Convert Difference to Cup Letter:

  • Less than 1" = AA Cup
  • 1" difference = A Cup
  • 2" difference = B Cup
  • 3" difference = C Cup
  • 4" difference = D Cup
  • 5" difference = DD/E Cup
  • 6" difference = DDD/F Cup
  • 7" difference = G Cup

Calculation Example:

Underbust = 32 inches, Bust = 36 inches

Band Size = 32 (already even number)

Cup Difference = 36 - 32 = 4 inches = D Cup

Result: 32D

US Bra Size Chart in Inches

Use this comprehensive chart to cross-reference your measurements with standard US bra sizes:

Band Size Underbust (in) AA Cup A Cup B Cup C Cup D Cup DD Cup
30 28-30 30-31 31-32 32-33 33-34 34-35 35-36
32 30-32 32-33 33-34 34-35 35-36 36-37 37-38
34 32-34 34-35 35-36 36-37 37-38 38-39 39-40
36 34-36 36-37 37-38 38-39 39-40 40-41 41-42
38 36-38 38-39 39-40 40-41 41-42 42-43 43-44
40 38-40 40-41 41-42 42-43 43-44 44-45 45-46
42 40-42 42-43 43-44 44-45 45-46 46-47 47-48

Understanding Sister Sizes

Sister sizes are alternative bra sizes that have the same cup volume but different band lengths. This concept is crucial for finding the perfect fit when your calculated size isn't quite right:

How Sister Sizes Work

When you go up one band size, go down one cup size to maintain the same cup volume. Conversely, when you go down one band size, go up one cup size. For example:

  • 34C sister sizes: 32D (tighter band, larger cup letter) or 36B (looser band, smaller cup letter)
  • 36D sister sizes: 34DD or 38C
  • 38B sister sizes: 36C or 40A

When to Try Sister Sizes:

  • The band feels too tight or too loose in your calculated size
  • Your size is between two band measurements
  • One brand's sizing runs different than another's
  • You're experiencing weight fluctuations
  • You want a different fit for specific bra styles

Signs Your Bra Doesn't Fit Properly

Knowing the signs of poor fit helps you identify when to adjust your size:

Band Fit Issues

  • Band Rides Up: Band size is too large; try a smaller band size
  • Band Too Tight: Leaves deep marks or causes discomfort; go up one band size
  • Bra Shifts Around: Band isn't providing adequate support; try a smaller band
  • Can't Fasten Comfortably: Band is too small; size up

Cup Fit Issues

  • Spillage/Overflow: Breasts overflow the cups (the "double boob" effect); go up a cup size
  • Gaping Cups: Empty space in cups or cups pucker; go down a cup size
  • Side Spillage: Breast tissue escapes under arms; try larger cup or different style
  • Underwire Discomfort: Wire sits on breast tissue instead of ribcage; try larger cup
  • Center Gore Not Flat: Fabric between cups doesn't touch chest; cup too small

Strap Issues

  • Straps Dig In: Band may be too loose, forcing straps to provide support; try smaller band
  • Straps Fall Down: May need to tighten straps or try different style
  • Straps Too Short/Long: Some bodies need different strap configurations

Common Measurement Mistakes to Avoid

⚠️ Avoid These Errors:

  • Measuring Over Clothing: Always measure with minimal clothing or in a non-padded bra for accuracy
  • Tape Not Level: The measuring tape must be parallel to the floor, not angled
  • Holding Breath: Breathe normally; holding your breath affects the measurement
  • Pulling Too Tight: The tape should be snug but not compressing your body
  • Wrong Bust Point: Measure at the fullest part, which may not be exactly at nipple level
  • Not Rounding Correctly: Band sizes only come in even numbers in US sizing
  • Ignoring Changes: Remeasure every 6 months or after weight changes of 10+ pounds

Bra Styles and Size Considerations

Different bra styles may fit differently even in the same size:

Full Coverage Bras

These cover more of the breast and typically run true to size. Best for larger cup sizes seeking maximum support and coverage.

Demi-Cup/Balconette Bras

These cover less of the breast and may require going up a cup size compared to your full coverage size, especially for fuller breasts.

Push-Up Bras

Padding reduces available cup space. You may need to go up one cup size compared to unpadded bras.

Sports Bras

Often sized S/M/L or use different sizing systems. Use brand-specific charts and prioritize compression and support over appearance.

Bralettes

Usually sized S/M/L without specific band/cup differentiation. Choose based on bust measurement and preferred fit (loose vs. snug).

When to Remeasure Your Bra Size

Your bra size changes throughout life. Remeasure in these situations:

  • Weight Changes: Gain or loss of 10+ pounds affects bust and band measurements
  • Pregnancy and Postpartum: Significant changes occur during and after pregnancy
  • Breastfeeding: Size fluctuates frequently; measure every few months
  • Hormonal Changes: Menstrual cycle, birth control, or menopause affect breast size
  • Age: Breast shape and tissue density change with age
  • Surgery or Medical Treatment: Any procedure affecting chest area requires remeasurement
  • Fit Issues: If bras that once fit well no longer do, remeasure
  • Regular Interval: Every 6-12 months as a general practice

Frequently Asked Questions

How do I measure my bra size in inches at home?
Measure your underbust (band size) by wrapping a measuring tape snugly around your ribcage directly under your breasts. Round to the nearest even number. Then measure around the fullest part of your bust. Subtract your band size from your bust measurement to find cup size: 1" difference = A cup, 2" = B cup, 3" = C cup, 4" = D cup, and so on. Use a soft fabric measuring tape and ensure it's level around your body.
What does the cup size letter mean in bra sizing?
Cup size letters (A, B, C, D, DD, etc.) represent the difference in inches between your bust measurement and band size. Each letter corresponds to a 1-inch difference: A = 1 inch, B = 2 inches, C = 3 inches, D = 4 inches, DD/E = 5 inches, and so on. The cup size indicates volume relative to the band size, not absolute breast size—a 32D has less volume than a 38D.
Why do bra sizes vary between brands?
Different brands use slightly different patterns, materials, and manufacturing processes, causing size variations. Some brands run small or large, and European brands use different sizing systems than US brands. Additionally, different bra styles (push-up, demi-cup, full coverage) fit differently even within the same brand. Always try on bras when possible and use brand-specific size charts.
How often should I measure my bra size?
Measure your bra size every 6-12 months as a baseline, and more frequently if you experience weight changes (10+ pounds), pregnancy, hormonal changes, or notice your current bras don't fit properly. Your bra size can change due to weight fluctuations, aging, hormones, medical conditions, or changes in physical activity levels.
What are sister sizes in bra fitting?
Sister sizes are alternative bra sizes with the same cup volume but different band sizes. When you go up one band size, you go down one cup size (and vice versa) to maintain cup volume. For example, 34C has sister sizes of 32D (smaller band, larger cup letter) and 36B (larger band, smaller cup letter). Sister sizes help you fine-tune fit when your calculated size isn't perfect.
Should I measure my bra size with or without a bra on?
For the most accurate measurements, measure without a bra or wearing only a non-padded, unlined bra that doesn't compress or add volume. Padded bras, push-up bras, and sports bras can affect measurements by adding artificial volume or compressing breast tissue. If you must wear a bra while measuring, choose the thinnest, most natural one you own.
Is a 34C the same as a 36B or 32D?
No, they have different cup volumes despite being related as sister sizes. A 34C has a specific cup volume designed for a 34-inch band. While 32D (smaller band, proportionally larger cup) and 36B (larger band, proportionally smaller cup) are sister sizes with similar volumes, the actual fit differs due to band tension and cup placement. Sister sizes are alternatives to try, not exact equivalents.

Tips for Finding the Perfect Bra Fit

Beyond measurements, these practical tips ensure optimal comfort and support:

Shopping and Trying On

  • Always Try Before Buying: Sizes vary by brand and style; in-store fitting is ideal
  • Start with Middle Hook: New bras should fit comfortably on the loosest hook, allowing you to tighten as they stretch
  • Scoop and Swoop: After fastening, lean forward and scoop all breast tissue into the cups for proper fit assessment
  • Move Around: Raise your arms, bend, and twist to ensure the bra stays in place
  • Check in a Mirror: View from all angles to assess band level, cup fit, and strap positioning
  • Wear Your Own Clothes: Try on bras under clothing similar to what you'll wear them with

Bra Care for Longevity

  • Hand Wash When Possible: Extends bra life and maintains shape better than machine washing
  • Use Lingerie Bags: If machine washing, always use a mesh lingerie bag
  • Air Dry Only: Never put bras in the dryer; heat damages elastic and padding
  • Rotate Bras: Don't wear the same bra two days in a row; allow elastic to recover
  • Store Properly: Don't fold cups inside each other; lay flat or hang by center gore
  • Replace Regularly: Replace bras every 6-12 months or when they lose support

Professional Fitting Services: Many lingerie stores and department stores offer free professional bra fittings. Consider getting professionally fitted at least once to validate your measurements and learn what proper fit feels like. Fitters can identify fit issues you might miss and recommend styles suited to your breast shape.

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