Bra Size Calculator

Q: Why does the same cup letter mean different volumes on different band sizes?

Cup size is based on the difference between your bust and band measurements, not a fixed volume. A D cup on a 32 band holds much less volume than a D cup on a 40 band. The band size sets the baseline, and the cup letter describes how much bigger the bust is compared to that baseline.

Your Recommended Bra Size

US / UK Size

32DD

EU Size

70E

FR / ES Size

85E

Band Size

Cup Size (US)

Avg Bust Measurement

37.0"

Bust-Band Difference

5.0"

Sister Sizes

Sister sizes have approximately the same cup volume. If your recommended size doesn't feel right, try one of these alternatives:

30DDD 32DD 34D

← Tighter band, larger cup letter | Looser band, smaller cup letter →

Fit Tips

Band Fit

The band should feel snug and level all around. You should be able to fit two fingers under the band.

Cup Fit

The cups should fully enclose breast tissue with no spillage or gaping. The center gore (front piece) should sit flat against your sternum.

Straps

Straps should be snug but not digging in. Most support comes from the band, not the straps.

International Size Conversion

US	UK	EU	FR / ES	IT	AU / NZ	JP

Your Measurements Overview

Cup Size Reference (US Sizing)

Difference (inches)	US Cup	UK Cup	EU Cup

Introduction

Finding the right bra size can be tricky. Studies show that up to 80% of people wear the wrong bra size, which can lead to discomfort, poor posture, and lack of support. Our Bra Size Calculator takes six key body measurements — three around your underbust and three around your bust — to give you an accurate, personalized size recommendation. Unlike simple two-measurement methods, this approach accounts for differences in breast shape and tissue distribution, giving you a much more reliable result.

The calculator provides your size in US, UK, EU, and other international sizing systems, along with sister sizes you can try if your recommended fit isn't quite right. It also adjusts for different body types, so everyone can get a useful starting point. Simply grab a soft measuring tape, follow the step-by-step guide below, and enter your numbers. In seconds, you'll have a clear recommendation plus helpful fit tips to make sure your next bra feels comfortable and supportive all day long. For a broader understanding of your body composition, you might also explore our Body Fat Calculator or Ideal Body Weight Calculator.

How to Use Our Bra Size Calculator

Enter your underbust and bust measurements below, and this calculator will give you your recommended bra size in US, UK, EU, and other international sizing systems, along with sister sizes and fit tips.

Measurement Units: Choose whether you want to enter your measurements in inches or centimeters. The calculator will adjust all fields to match your choice.

Body Type: Select the option that best describes your body — assigned female at birth (AFAB), assigned male at birth (AMAB), or not listed. This helps the calculator adjust for differences in ribcage shape and breast tissue.

Loose Underbust: Wrap a soft measuring tape around your ribcage just below your breasts. Keep the tape comfortably loose so you can slide a finger underneath. Enter that number here.

Snug Underbust: Measure in the same spot below your breasts, but this time pull the tape firm against your skin. It should feel snug but not uncomfortable.

Tight Underbust: Measure in the same spot one more time. Pull the tape as tight as you can and breathe all the air out of your lungs. Enter that number here.

Standing Bust: Stand up straight with your arms at your sides. Wrap the tape around the fullest part of your bust and enter the measurement.

Leaning Bust: Bend forward at the waist so your back is parallel to the floor. Let your bust hang naturally and measure around the fullest point.

Lying Bust: Lie flat on your back and measure around the fullest part of your bust. This helps capture how your breast tissue distributes in different positions.

Once all six measurements are entered, click Calculate to see your recommended bra size, sister sizes, an international size conversion table, and personalized fit tips. Click Reset at any time to clear your entries and start over.

How to Find Your Bra Size

Wearing the wrong bra size is extremely common. Studies suggest that up to 80% of people wear a bra that doesn't fit properly. A poorly fitting bra can cause back pain, shoulder pain, skin irritation, and general discomfort throughout the day. This bra size calculator uses six body measurements to give you an accurate, personalized size recommendation across multiple international sizing systems.

Why Six Measurements?

Most simple bra size charts only use two measurements — one for the band and one for the bust. While that can get you in the right ballpark, it often misses important details about your unique body shape. This calculator asks for three underbust measurements (loose, snug, and tight) and three bust measurements (standing, leaning, and lying down). Each measurement captures different information:

Loose underbust shows your ribcage size with comfortable breathing room.
Snug underbust reflects how a well-fitting band should feel against your body.
Tight underbust reveals the smallest your ribcage can go, which helps determine how much flexibility you have in band sizing.
Standing bust measures your bust in a natural, upright position.
Leaning bust captures your full breast volume by letting gravity pull tissue forward, which is especially helpful for people with softer or more projected breast tissue.
Lying bust shows how your tissue distributes when supported from below, which gives a more balanced picture of cup size.

By combining all six measurements, the calculator produces a weighted average that accounts for differences in breast shape, tissue firmness, and projection. If you're also interested in other body proportion metrics, our Waist to Hip Ratio Calculator and Waist to Height Ratio Calculator offer complementary insights.

Understanding Band Size

The band is the numbered part of your bra size (like the "32" in 32D). It corresponds to the circumference of your ribcage just below your breasts. A good-fitting band should feel snug and provide most of the bra's support. The calculator averages your snug and tight underbust measurements, then rounds to the nearest even number, since bands are sold in even-numbered increments (28, 30, 32, 34, and so on).

Understanding Cup Size

The cup is the letter part of your bra size (like the "D" in 32D). It is not a fixed volume — it is based on the difference between your bust measurement and your band size. A D cup on a 32 band is a much smaller volume than a D cup on a 40 band. Each inch of difference between bust and band roughly equals one cup size. For example, a 1-inch difference is an A cup, a 2-inch difference is a B cup, and so on.

What Are Sister Sizes?

Sister sizes are bra sizes that share roughly the same cup volume but use a different band and cup letter combination. For example, 32DD, 34D, and 30DDD are all sister sizes. If your recommended size feels slightly off, trying a sister size can help. Going down in band size means going up in cup letter, and going up in band size means going down in cup letter. The total volume of the cup stays about the same.

International Sizing Differences

Bra sizing is not universal. The US, UK, EU, French, Italian, Australian, and Japanese systems all use different numbers and letters. For example, a US 32DD is the same as a UK 32DD, an EU 70E, and a French 85E. The conversion table provided with your results makes it easy to shop from brands that use any of these systems.

Body Type Considerations

This calculator includes a body type option because ribcage shape and breast tissue characteristics can vary. People assigned male at birth (AMAB) tend to have wider ribcages and different tissue distribution compared to people assigned female at birth (AFAB). The calculator makes small adjustments based on your selection to improve accuracy. Choose whichever option best describes your body. For related body metrics, you may find our BSA Calculator or Lean Body Weight Calculator helpful in understanding how your frame and composition compare.

Tips for Accurate Measuring

For the best results, measure yourself while wearing a thin, unpadded bra or no bra at all. Use a soft measuring tape and keep it level all the way around your body. Stand in front of a mirror to check that the tape hasn't shifted. Take each measurement twice and use the average if the numbers differ slightly. Avoid measuring right after exercise, as temporary swelling can change your results.

When to Remeasure

Your bra size can change over time due to weight changes, hormonal shifts, pregnancy, aging, or changes in muscle mass. It's a good idea to remeasure yourself every 6 to 12 months, or whenever your current bras start to feel uncomfortable. A bra that fit perfectly a year ago may no longer be the right size today. If you're tracking body changes related to pregnancy, our Pregnancy Weight Gain Calculator and Due Date Calculator can be valuable companions. For those monitoring weight fluctuations more broadly, our Weight Loss Calculator and Calorie Calculator can help you understand how shifts in weight may affect your measurements over time.

Frequently asked questions

How accurate is this bra size calculator?

This calculator uses six measurements instead of the usual two, so it is more accurate than most basic bra size charts. It accounts for differences in breast shape, tissue firmness, and projection. That said, no calculator can replace trying on bras in person. Use your result as a strong starting point, then adjust based on how the bra actually feels.

What tools do I need to measure myself?

You need a soft, flexible measuring tape — the kind used for sewing. Do not use a stiff metal tape measure. If you don't have a soft tape, you can wrap a piece of string around your body, mark it, and then measure the string against a ruler.

Should I wear a bra while measuring?

It is best to measure while wearing a thin, unpadded bra or no bra at all. Padded or push-up bras will add extra volume and throw off your bust measurements, leading to an incorrect size.

Why do I need three underbust measurements instead of just one?

The three underbust measurements (loose, snug, and tight) show how much padding and compressibility your ribcage area has. This helps the calculator pick the best band size. Some people have more soft tissue around their ribs, while others have a very firm ribcage. Three measurements capture that difference.

Why do I need three bust measurements instead of just one?

Breast tissue shifts depending on your position. Standing, leaning, and lying measurements each capture a different aspect of your breast shape and volume. Averaging these gives a much more reliable cup size than any single measurement alone.

What does the leaning bust measurement do?

The leaning bust measurement captures your full breast volume by letting gravity pull your tissue forward. This is especially important for people with soft or projected breast tissue, since a standing measurement alone might underestimate cup size.

Can I use this calculator if I am a man or non-binary person?

Yes. The calculator includes a body type option that adjusts for different ribcage shapes and tissue characteristics. Select the option that best matches your body. Anyone who needs a bra can use this tool.

What does the AMAB body type option change?

People assigned male at birth often have wider ribcages and different breast tissue distribution. The AMAB option makes small adjustments to the band calculation and how the bust measurements are weighted so the result better fits that body type.

What if my result falls between two sizes?

Try both sizes. If the band feels too tight, go up one band size and down one cup letter. If the band feels too loose, go down one band size and up one cup letter. The sister sizes shown in your results make this easy.

Why does the same cup letter mean different volumes on different band sizes?

Cup size is based on the difference between your bust and band measurements, not a fixed volume. A D cup on a 32 band holds much less volume than a D cup on a 40 band. The band size sets the baseline, and the cup letter describes how much bigger the bust is compared to that baseline.

How do I know if my bra band is the right size?

A well-fitting band should be snug and level all the way around your body. You should be able to slide two fingers under the band but not your whole hand. The band should not ride up in the back. If it does, the band is too loose.

How do I know if my bra cup is the right size?

The cup should fully contain your breast tissue with no spillage over the top or sides and no wrinkling or gaping. The center piece (called the gore) between the cups should sit flat against your chest.

How often should I recalculate my bra size?

You should remeasure every 6 to 12 months. Your size can change due to weight gain or loss, hormonal changes, pregnancy, aging, or changes in fitness level. If your current bra starts feeling uncomfortable, it is time to remeasure.

Can I switch between inches and centimeters?

Yes. Use the unit toggle at the top of the calculator to switch between inches and centimeters. The calculator will automatically convert any values you have already entered.

Why is my underbust measurement larger than my bust measurement error showing?

Your bust measurement should always be equal to or larger than your underbust measurement. If the calculator shows this error, double-check that you are measuring in the right spots. The underbust goes just below your breasts, and the bust goes around the fullest part of your chest.

Do different bra brands fit the same even in the same size?

No. Bra sizing is not perfectly standardized across brands. Two bras labeled 34C can fit quite differently depending on the brand, style, and materials. Use your calculated size as a starting point and always try before you buy when possible.

What is the difference between US and UK cup sizes?

US and UK sizes use the same band numbers but different cup letter sequences after D. For example, a US DDD is the same as a UK E. The calculator shows both systems so you can shop from any brand confidently.

What is the EU bra sizing system?

The EU system uses centimeter-based band numbers (like 70, 75, 80) instead of inch-based numbers. The cup letters also follow a simpler A, B, C, D, E, F sequence without double letters like DD. The conversion table in your results shows exactly how your size translates.

Can I use this calculator during pregnancy or while nursing?

You can, but keep in mind that your size may change frequently during pregnancy and breastfeeding. Measure yourself as you normally would and recalculate often. You may want to look for bras with stretch or adjustable features during this time.

What if my measurements don't match any standard size?

The calculator rounds to the nearest standard size. If your measurements fall far outside typical ranges, the closest available size may not be a perfect fit. In that case, consider trying sister sizes or looking into brands that specialize in extended or custom sizing.