Use this free Bra Size Calculator to calculate your bra size from bust and underbust measurements, compare international sizes, and find useful sister-size options.
Introduction to the Bra Size Calculator
Finding the right bra size can be surprisingly difficult. Different brands use different sizing systems, breast shapes vary from person to person, and a measurement taken from only one point may not always provide a reliable estimate. The Bra Size Calculator is designed to make the process easier by analyzing multiple measurements and providing a practical starting size for bra shopping.
This Bra Size Calculator supports both quick and detailed measurement methods. The Quick 2-Point Mode is useful when you only have your underbust and bust measurements, while the Pro 6-Point Precision Mode uses loose, snug, and tight underbust measurements together with standing, leaning, and lying bust measurements. This gives the calculator more information about ribcage size, breast volume, and projection.
The Bra Size Calculator also supports inches and centimeters, making it convenient for users around the world. After calculation, the tool can provide international size conversions for US/Canada, UK, EU, Japan, Australia/New Zealand, and France/Spain sizing systems.
Instead of giving you only one number and letter, the Bra Size Calculator is designed to provide additional fitting information, including sister sizes, calculation steps, and practical troubleshooting guidance. Whether you are buying a new everyday bra, comparing international bra sizes, or simply trying to understand your measurements, this tool can give you a useful starting point.
A calculator cannot replace a professional bra fitting or guarantee that every brand will fit identically, but the Bra Size Calculator can help you understand your measurements before making a purchase.
About the Bra Size Calculator
Choosing the correct bra size is not simply a matter of measuring around your body and selecting a letter from a chart. A comfortable bra needs to work with your ribcage, breast volume, breast projection, and overall shape. That is why many people discover that the size they have worn for years is not necessarily the size that fits them best.
The Bra Size Calculator solves this problem by turning several body measurements into a practical bra-size estimate. Instead of relying exclusively on a single bust measurement, the tool can evaluate multiple underbust and bust measurements. This gives you more information about how your measurements relate to the recommended band and cup size.
The Pro 6-Point Precision Mode is particularly useful for users who want a more detailed calculation. It uses loose underbust, snug underbust, and tight underbust measurements to evaluate the ribcage area. It also uses standing bust, leaning bust, and lying bust measurements to provide additional information about breast volume and projection.
The Bra Size Calculator includes a Quick 2-Point Mode for users who want a simpler calculation. This is helpful when you are shopping and only have basic measurements available. Although a two-measurement method is less detailed than the six-point approach, it can still provide a useful estimate.
Another important advantage of the Bra Size Calculator is international sizing support. A bra labeled 32D in one sizing system may not have the same label in another country. The tool therefore provides regional conversions to help users understand equivalent sizes when shopping from international brands.
The Bra Size Calculator also introduces the concept of sister sizes. Sister sizes have different band and cup labels but are designed around similar cup volume. For example, moving down one band size generally requires moving up one cup step, while moving up one band size generally requires moving down one cup step. This can be useful when your calculated size is unavailable or when you need to adjust the band for comfort.
The tool also provides fitting guidance for common problems. If the cups spill over, the band rides upward, the cups gap, or the underwire feels uncomfortable, the diagnostic section can help you identify possible adjustments.
Most importantly, the Bra Size Calculator should be treated as a starting point rather than an absolute rule. Bra construction, fabric stretch, cup shape, underwire width, brand sizing, and individual breast shape can all affect fit. Two bras with the same labeled size can feel completely different.
Use the Bra Size Calculator to understand your measurements, compare sizes, explore sister sizes, and make more informed shopping decisions.
US & Canada Bra Size Chart
Use this US and Canada bra size chart to compare common band and cup sizes. Bra sizing can vary between brands, so use the chart as a general reference.
| Band | AA | A | B | C | D | DD/E | DDD/F | G | H |
|---|---|---|---|---|---|---|---|---|---|
| 28 | 28AA | 28A | 28B | 28C | 28D | 28DD | 28DDD | 28G | 28H |
| 30 | 30AA | 30A | 30B | 30C | 30D | 30DD | 30DDD | 30G | 30H |
| 32 | 32AA | 32A | 32B | 32C | 32D | 32DD | 32DDD | 32G | 32H |
| 34 | 34AA | 34A | 34B | 34C | 34D | 34DD | 34DDD | 34G | 34H |
| 36 | 36AA | 36A | 36B | 36C | 36D | 36DD | 36DDD | 36G | 36H |
| 38 | 38AA | 38A | 38B | 38C | 38D | 38DD | 38DDD | 38G | 38H |
| 40 | 40AA | 40A | 40B | 40C | 40D | 40DD | 40DDD | 40G | 40H |
| 42 | 42AA | 42A | 42B | 42C | 42D | 42DD | 42DDD | 42G | 42H |
| 44 | 44AA | 44A | 44B | 44C | 44D | 44DD | 44DDD | 44G | 44H |
UK Bra Size Chart
This UK bra size chart shows common UK band and cup combinations. UK cup sizing uses a different progression from some US and European systems.
| Band | AA | A | B | C | D | DD | E | F | FF | G | GG |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 28 | 28AA | 28A | 28B | 28C | 28D | 28DD | 28E | 28F | 28FF | 28G | 28GG |
| 30 | 30AA | 30A | 30B | 30C | 30D | 30DD | 30E | 30F | 30FF | 30G | 30GG |
| 32 | 32AA | 32A | 32B | 32C | 32D | 32DD | 32E | 32F | 32FF | 32G | 32GG |
| 34 | 34AA | 34A | 34B | 34C | 34D | 34DD | 34E | 34F | 34FF | 34G | 34GG |
| 36 | 36AA | 36A | 36B | 36C | 36D | 36DD | 36E | 36F | 36FF | 36G | 36GG |
| 38 | 38AA | 38A | 38B | 38C | 38D | 38DD | 38E | 38F | 38FF | 38G | 38GG |
| 40 | 40AA | 40A | 40B | 40C | 40D | 40DD | 40E | 40F | 40FF | 40G | 40GG |
| 42 | 42AA | 42A | 42B | 42C | 42D | 42DD | 42E | 42F | 42FF | 42G | 42GG |
| 44 | 44AA | 44A | 44B | 44C | 44D | 44DD | 44E | 44F | 44FF | 44G | 44GG |
International Bra Size Conversion Chart
Compare common US, UK, EU, Japan, Australia and France band-size systems with this international bra size conversion chart.
| US / UK | EU | Japan | AU / NZ | France |
|---|---|---|---|---|
| 28 | 60 | 60 | 6 | 75 |
| 30 | 65 | 65 | 8 | 80 |
| 32 | 70 | 70 | 10 | 85 |
| 34 | 75 | 75 | 12 | 90 |
| 36 | 80 | 80 | 14 | 95 |
| 38 | 85 | 85 | 16 | 100 |
| 40 | 90 | 90 | 18 | 105 |
| 42 | 95 | 95 | 20 | 110 |
| 44 | 100 | 100 | 22 | 115 |
Bra Cup Size Difference Chart
The bust-to-underbust difference can provide a starting point for estimating cup size. Actual sizing varies by brand and sizing system.
| Bust − Underbust | Approximate Cup |
|---|---|
| 0 inch | AA |
| 1 inch | A |
| 2 inches | B |
| 3 inches | C |
| 4 inches | D |
| 5 inches | DD / E |
| 6 inches | DDD / F |
| 7 inches | G |
| 8 inches | H |
| 9 inches | I |
| 10 inches | J |
Bra Sister Size Chart
Use this sister size chart when you want to compare a smaller or larger band with approximately similar cup volume.
| Current Size | Smaller Band | Larger Band |
|---|---|---|
| 30D | 28DD | 32C |
| 32C | 30D | 34B |
| 32D | 30DD | 34C |
| 34C | 32D | 36B |
| 34D | 32DD | 36C |
| 36C | 34D | 38B |
| 36D | 34DD | 38C |
| 38C | 36D | 40B |
| 38D | 36DD | 40C |
| 40C | 38D | 42B |
| 40D | 38DD | 42C |
Bra Size Calculator Features
- Pro 6-Point Precision Mode: Uses three underbust and three bust measurements to provide a more detailed size estimate.
- Quick 2-Point Mode: Provides a faster calculation when only basic underbust and bust measurements are available.
- Inches and Centimeters: Switch between Imperial and Metric measurements without manually converting values.
- Projection Analysis: Compares standing and leaning measurements to provide additional information about breast projection.
- International Size Conversion: Displays estimated equivalents for US/Canada, UK, EU, Japan, Australia/New Zealand, and France/Spain sizing systems.
- Sister Size Calculator: Shows alternative tighter-band and looser-band options while considering cup-volume changes.
- Step-by-Step Results: Explains how the measurements are processed so users can understand the calculation instead of receiving an unexplained result.
- Fit Diagnostic Guidance: Provides practical suggestions for common issues such as cup spillage, gaping, band riding, and wire discomfort.
- Mobile-Friendly Design: The Bra Size Calculator is designed to work across smartphones, tablets, and desktop screens.
- Copy, Print, and Reset Tools: Easily save or share your calculated result, print the result, or start a new calculation.
How the Bra Size Calculator Works
The Bra Size Calculator processes your measurements in several stages. First, it identifies the selected measurement system. If centimeters are selected, measurements are converted to inches using the standard conversion formula:
Inches = Centimeters ÷ 2.54
For the Pro 6-Point method, the calculator evaluates the loose, snug, and tight underbust measurements to estimate a practical band size. The difference between the snug and tight measurements can provide additional information about how much compression may be comfortable.
The bust measurements are then evaluated. The standing, leaning, and lying measurements provide different views of breast volume. The leaning measurement can be especially useful because leaning forward allows breast tissue to extend naturally.
For users with a larger difference between standing and leaning measurements, the calculator can use an averaged effective bust measurement:
Effective Bust = (Standing Bust + Leaning Bust + Lying Bust) ÷ 3
For a smaller projection difference, the leaning measurement can be used as the primary effective bust measurement.
The next stage calculates the difference between the effective bust and target band:
Cup Differential = Round(Effective Bust − Band Size)
The resulting differential is mapped to a cup progression. The calculator then converts the baseline result into other regional sizing systems and generates sister-size alternatives.
Because real-world bra fitting involves more variables than mathematics alone, the Bra Size Calculator provides an estimated starting point rather than a guaranteed fit.
How to Use the Bra Size Calculator
- Select your preferred measurement system: inches or centimeters.
- Choose Pro 6-Point Precision Mode if you want a detailed calculation.
- Choose Quick 2-Point Mode if you only have basic measurements.
- Measure your underbust according to the instructions provided by the tool.
- For precision mode, enter your loose, snug, and tight underbust measurements.
- Measure your standing, leaning, and lying bust measurements.
- Enter each measurement carefully and make sure the units are correct.
- Select the calculation option to generate your result.
- Review your recommended size and international conversions.
- Check the sister sizes if you want a tighter or more relaxed band option.
- Review the step-by-step calculation to understand how your result was generated.
- Use the fitting diagnostic section if you are experiencing cup, band, or wire problems.
For the most useful result, take measurements while wearing little or no clothing that could significantly change the measurement. Keep the measuring tape level and avoid pulling it unnecessarily tight.
Bra Size Calculator Example Calculations
Consider a user measuring in inches with the following Pro 6-Point measurements:
- Loose Underbust: 32.5 inches
- Snug Underbust: 31.5 inches
- Tight Underbust: 29.5 inches
- Standing Bust: 36 inches
- Leaning Bust: 38 inches
- Lying Bust: 36.5 inches
First, the calculator evaluates the snug underbust measurement. A value of 31.5 inches is rounded to approximately 32 inches. The difference between the snug and tight measurements is:
31.5 − 29.5 = 2 inches
Because the difference reaches the two-inch threshold, the algorithm treats the ribcage as having some compressibility and evaluates the appropriate even band size.
Next, the calculator compares the standing and leaning bust measurements:
38 − 36 = 2 inches
Because the projection delta is not greater than 2.5 inches, the leaning measurement can be used as the effective bust measurement under the stated algorithm.
Therefore:
Effective Bust = 38 inches
The cup differential is then estimated by comparing the effective bust with the target band:
38 − 32 = 6 inches
A six-inch differential corresponds to the appropriate cup progression in the calculator’s mapping system. The tool then produces the baseline result and translates it into supported international sizing systems.
A second example demonstrates the centimeter option. Suppose a user enters an underbust measurement of 80 cm and a bust measurement of 95 cm. The calculator first converts the measurements:
80 ÷ 2.54 ≈ 31.50 inches
and
95 ÷ 2.54 ≈ 37.40 inches
The converted values can then be evaluated using the same sizing process.
These examples demonstrate why the Bra Size Calculator is more useful when accurate measurements are entered. A small measurement error can change the estimated band or cup result, so users should measure carefully and repeat measurements when necessary.
Remember that the calculated size is a starting recommendation. Actual fit can vary depending on the bra’s construction, brand, fabric, cup shape, underwire, and individual breast shape.
Key Concept Guide: Understanding Bra Sizes
Band Size
The band is the number portion of a bra size, such as 30, 32, 34, or 36. It represents the approximate size of the ribcage area around the torso. The band provides much of the bra’s support, so it should feel secure without causing significant discomfort.
A band that is too loose may ride upward on the back. A band that is too tight may create excessive pressure or discomfort. The Bra Size Calculator uses underbust measurements to estimate an appropriate starting band.
Cup Size
The cup letter represents cup volume relative to the band rather than an absolute breast size. This is an important concept because a D cup on one band size does not have the same volume as a D cup on every other band size.
For example, sister-size relationships demonstrate why cup letters cannot be interpreted independently from band numbers.
Bust Measurement
Bust measurements are taken around the fullest part of the breasts. Different measurement positions can produce different results because breast tissue changes position when standing, leaning, or lying down.
The Bra Size Calculator uses these differences to provide a more detailed estimate.
Underbust Measurement
The underbust measurement is taken around the torso directly underneath the breasts. It is especially important for determining band size.
The tool uses loose, snug, and tight measurements in its precision mode because these measurements can provide more information than a single underbust measurement.
Breast Projection
Breast projection describes how much the breast tissue extends outward from the chest. Some people have more projected breasts, while others have shallower breast profiles.
The difference between standing and leaning measurements can provide useful clues about projection. A larger difference may indicate that more tissue becomes measurable when leaning forward.
Sister Sizes
Sister sizes are alternative bra sizes that have similar cup volume but different band measurements. If you need a tighter band, you generally move down one band size and up one cup step. If you need a looser band, you generally move up one band size and down one cup step.
For example, depending on the starting size and sizing system, a 32D may have a sister-size relationship with 34C or 30DD.
Sister sizes should not be viewed as identical fits. Changing the band also changes how the cup sits on the body, so the cup shape and underwire may feel different.
International Bra Sizing
Bra sizes are not standardized globally. US, Canadian, UK, European, Japanese, Australian, New Zealand, French, and Spanish systems may use different numbers or cup-letter progressions.
The Bra Size Calculator helps simplify this process by presenting regional equivalents. However, international conversions should still be checked against the specific manufacturer’s size chart because brands can vary.
Cup Spillage
If breast tissue spills over the top or sides of the cup, the cup may be too small or the cup shape may not match the breast shape. Increasing the cup size can sometimes help, but the correct solution depends on the overall fit.
Cup Gaping
Cup gaping does not always mean that the cup is too large. It can occur when the cup shape does not match the breast shape, particularly with molded or rigid cups.
Band Riding Up
If the back band moves upward, the band may be too loose. Adjusting to a smaller band can improve support, although cup volume must also be considered.
Underwire Comfort
Underwires should generally sit around the breast tissue rather than directly on it. Poking or discomfort may indicate an incorrect size, unsuitable wire width, or a cup shape that does not match the wearer.
Tips and Best Practices for Accurate Bra Measurements
For the best results from the Bra Size Calculator, measurement technique matters. Even a sophisticated calculator cannot compensate for inaccurate measurements.
Use a flexible measuring tape. Keep it horizontal around your body and avoid twisting it. When measuring the underbust, make sure the tape sits directly underneath the breast tissue.
Take the loose underbust measurement without deliberately compressing the ribcage. For the snug measurement, pull the tape comfortably against the body without forcing it. For the tight measurement, apply firmer tension while remaining within a comfortable measurement technique.
When measuring the bust, keep your posture natural. For the standing measurement, stand upright without pushing the breasts upward or inward. For the leaning measurement, bend approximately 90 degrees so that the breasts hang naturally. For the lying measurement, lie comfortably on your back and take the measurement around the fullest area.
Repeat measurements if the numbers appear unusual. Taking each measurement two or three times and using consistent technique can reduce accidental errors.
Do not measure over a thick sweatshirt or padded clothing. Clothing can add several centimeters or inches to the result.
If possible, measure when your breasts are in their normal state rather than immediately after temporary swelling or compression. However, natural body changes can still affect measurements, so consider the result an estimate.
When shopping, do not assume that the same labeled size will fit every brand. Use your calculated result as a starting point and compare it with the manufacturer’s own size guide.
Use sister sizes intelligently. If your band feels good but the cup is too small, changing only the cup may be more appropriate than changing the entire size. If the band is too loose, moving to a smaller band while increasing the cup letter can preserve approximately similar cup volume.
Finally, pay attention to how the bra actually fits. Comfort, support, cup coverage, band stability, and underwire placement are often more important than matching a particular size label.
Frequently Asked Questions About the Bra Size Calculator
How accurate is a Bra Size Calculator?
A Bra Size Calculator can provide a useful starting estimate, but it cannot guarantee a perfect fit. Bra sizing is affected by measurement technique, breast shape, projection, bra construction, brand sizing, fabric stretch, and personal comfort preferences.
The Pro 6-Point method can provide more information than a basic two-measurement calculation because it considers multiple underbust and bust measurements. However, the final size should still be treated as an estimate.
If a calculated size does not feel comfortable, compare nearby sizes and evaluate the band, cups, and underwire separately. Manufacturer-specific size charts can also differ.
How do I measure for a bra size at home?
To measure at home, you need a flexible measuring tape. Start by measuring around the ribcage directly underneath the breasts. For the precision method, record loose, snug, and tight underbust measurements.
Next, measure around the fullest part of the breasts while standing. For the Pro 6-Point method, also take a leaning measurement while bending forward approximately 90 degrees and a lying measurement while lying comfortably on your back.
Keep the measuring tape level and avoid pulling it excessively tight. Enter the measurements into the Bra Size Calculator using the correct unit system.
For the best results, repeat each measurement and use consistent positioning. Remember that the calculated result is a starting point rather than a guarantee that every bra will fit identically.
What is the difference between US, UK, EU, and other bra sizes?
Different countries use different bra sizing conventions. Band numbers may be expressed differently, and cup-letter progressions can vary between systems.
For example, a UK bra size and an EU bra size may use different band numbers even though they represent approximately comparable body measurements. Australia and New Zealand also use a different numerical band system.
The Bra Size Calculator provides international conversion estimates to make comparison easier. However, always check the individual brand’s sizing chart before purchasing because conversion systems are not perfectly standardized.
When buying internationally, pay attention to both the band and cup. Converting only one part of the size can result in an incorrect selection.
What are bra sister sizes?
Sister sizes are sizes with different band numbers but approximately similar cup volume. They are useful when the calculated size is unavailable or when you need to adjust the band fit.
If you move down one band size, you generally move up one cup letter. If you move up one band size, you generally move down one cup letter.
For example, a 32D may have sister-size relationships with 30DD and 34C, depending on the sizing system. These sizes do not necessarily feel identical because the band circumference, cup dimensions, wire geometry, and bra construction can change.
The Bra Size Calculator provides sister-size suggestions so you can explore alternatives instead of assuming there is only one possible size.
Why does my calculated bra size not fit?
There are several reasons your calculated size may not fit. Your measurements may have been taken incorrectly, the bra brand may use a different sizing method, or the bra’s cup shape may not match your breast shape.
A cup that gaps does not automatically mean the cup is too large. Similarly, cup spilling does not always mean that simply increasing the cup letter will solve the problem.
Check the band first. It should remain relatively stable around your torso rather than riding significantly upward. Then check the cups for spilling, gaping, wrinkling, or tissue being compressed.
Underwire placement is also important. If the wire sits directly on breast tissue or pokes uncomfortably, the problem may involve cup width or shape rather than size alone.
Use the Bra Size Calculator as a starting point and combine the result with actual fit observations. If necessary, try the recommended size, one sister size in either direction, and different cup styles.
Conclusion: Use the Bra Size Calculator as Your Starting Point
Finding a comfortable bra size does not have to be confusing. The Bra Size Calculator brings multiple measurements, sizing calculations, international conversions, sister sizes, and practical fitting guidance together in one convenient tool.
The Pro 6-Point Precision Mode is designed for users who want a more detailed measurement process, while Quick 2-Point Mode provides a faster alternative. Support for inches and centimeters makes the tool accessible to users in different countries, and international conversion results make online shopping easier.
The most important thing to remember is that a size label is only a starting point. Your individual breast shape, projection, the bra’s construction, brand sizing, and personal comfort all influence the final fit.
Use the Bra Size Calculator to understand your measurements, compare potential sizes, explore sister sizes, and make more informed decisions when shopping for bras. If one size does not feel right, do not assume the calculator has failed. Try nearby sizes and different bra styles while paying attention to how the band, cups, and underwire actually fit.
Explore More Free Calculator Tools
The Love Calculator is a fun compatibility tool that generates an entertaining relationship score from two names. It is designed for casual use and provides a simple way to explore compatibility.
The Shoe Size Conversion Tool helps convert footwear sizes between different international sizing systems. It can be useful when shopping for shoes from international stores or comparing US, UK, EU, and other size standards.
The Time Zone Calculator helps compare times between different locations. It can be useful for international communication, travel planning, remote work, meetings, and scheduling.
The Day Counter Calculator calculates the number of days between dates. It can help with event planning, deadlines, project schedules, anniversaries, and other date-related calculations.
The Date Calculator helps users add or subtract days, weeks, months, or years from a selected date. It is useful for planning future dates, calculating deadlines, and determining date intervals.