Bra Size Calculator

Use this Bra Size Calculator to estimate your starting bra size from your underbust and bust measurements. Enter your measurements in inches or centimetres and choose USA/Canada, UK, Europe, or France to see your estimated band size, cup size, international equivalents, and nearby sister sizes.

Bra sizing is not completely standardized between brands, countries, or styles, so no online measurement can guarantee a perfect fit. Use the calculated size as a practical starting point, then check the band, cups, straps, and centre gore when trying on a bra. The guide below also explains how to measure bra size, convert international sizes, understand cup sizes, and use sister sizes when a band or cup feels slightly wrong.

How to Measure Bra Size

You need two measurements to get a useful starting bra size: your underbust measurement and your full bust measurement. Use a flexible measuring tape if possible. Take the measurements while standing naturally and keep the tape parallel to the floor.

It is usually easiest to measure while wearing no bra or a thin, unpadded bra that does not significantly change the shape or volume of the bust. Heavy padding can add inches to the bust measurement and affect the calculated cup size.

Step 1: Measure Your Underbust

Wrap the tape directly under the breast tissue where the bra band normally sits. Keep it level around your back. Pull the tape snug enough that it does not slide down, but do not pull so tightly that it compresses your ribs uncomfortably.

Record the measurement without deliberately adding extra inches. The calculator uses that measurement to estimate the band size that is closest to your ribcage measurement.

Step 2: Measure the Fullest Part of Your Bust

Place the measuring tape around the fullest part of the bust. Keep the tape level across your back and relaxed across the breast tissue. The tape should touch the body without flattening the breasts.

Record the number in inches or centimetres. Enter that value as the Full Bust Measurement in the calculator.

Step 3: Calculate Your Starting Size

The calculator converts your underbust into an estimated band size and compares your full bust measurement with that band. The difference determines the estimated cup progression. It then converts the result to the sizing system you selected.

Do not treat the calculated size as an absolute answer. Bra sizing is affected by brand grading, fabric stretch, cup shape, wire width, breast shape, and personal fit preference. Bravissimo specifically notes that brands can fit differently and recommends treating conversion charts as a starting point rather than assuming every bra with the same label fits identically.

How Bra Sizing Works

A traditional bra size contains two parts. The number represents the band size, while the letter represents the cup size. A size such as 34D therefore combines a 34 band with a D cup.

The two parts are connected. A D cup is not one fixed breast volume across every band. A 32D has less cup volume than a 36D. This is why comparing only cup letters can be misleading.

The cup volume generally increases as either the band or cup designation increases. This relationship also explains why sister sizes can provide similar cup capacity with a different band size.

How to Find Your Band Size

Your band provides much of the support in a properly fitted bra, so measuring the ribcage carefully is important. This calculator uses a snug underbust measurement and maps it to the nearest even-numbered U.S./UK band as a practical starting point.

For example, an underbust near 32 inches generally points toward a 32 band as a starting size. An underbust around 33.5 to 34 inches generally points toward a 34 band.

Some traditional fitting methods add four or five inches to the underbust before choosing a band. Many modern specialty-bra fitting systems instead begin closer to the actual snug ribcage measurement because modern bands contain elastic. That is one reason two online calculators can give different answers from the same measurements.

How to Find Your Cup Size

Cup size is estimated from the difference between the full bust measurement and the fitted band measurement. In a common inch-based progression, approximately one inch of difference represents an A cup, two inches a B cup, three inches a C cup, and four inches a D cup.

After D, cup lettering becomes particularly important because the United States, United Kingdom, and Europe do not all use the same progression. That is why the calculator does not simply copy the same cup letter into every country's result.

Bra Size Chart

A size chart is useful for understanding how band numbers correspond across international sizing systems. The following table shows common U.S./UK bands and their approximate European and French equivalents.

International Bra Size Conversion

Band conversion is relatively straightforward, but cup conversion becomes more complicated after D. A U.S. size should not automatically be converted to the same cup letters in the UK or Europe.

For example, common conversion charts show U.S. DD/E as approximately UK DD and EU E. A U.S. DDD/F is commonly equivalent to UK E and EU F. Higher cup sizes continue to diverge because the UK system uses double letters such as FF, GG, and HH while European cup progression typically continues alphabetically.

Bare Necessities publishes conversion charts showing these differences, and Bravissimo similarly warns that conversion should be treated as a starting point because individual brands may fit differently.

US and Canada Bra Sizes

U.S. and Canadian retailers commonly use the same basic band numbering, but cup labels above D vary between brands. You may see sizes written as DD, DDD, F, G, H, I, and higher, while another brand may use combinations such as DD/E or DDD/F.

UK Bra Sizes

UK sizing commonly progresses through D, DD, E, F, FF, G, GG, H, HH, J, JJ and higher sizes. This progression differs from most U.S. and European systems.

European Bra Sizes

European bands are commonly labelled in 5-centimetre increments such as 65, 70, 75, 80, and 85. Cup lettering generally progresses alphabetically after D rather than using the UK's repeated double-letter sequence.

French Bra Sizes

French band numbers are typically 15 higher than the corresponding EU band. For example, a U.S./UK 32 band commonly corresponds to EU 70 and French 85. A 36 band commonly corresponds to EU 80 and French 95.

Bra Sister Sizes

Sister sizes are nearby bra sizes with approximately similar cup volume but different band sizes. When the band becomes one step smaller, the cup typically needs to move one step larger. When the band becomes one step larger, the cup typically moves one step smaller.

For example, common sister sizes around 34C include 32D and 36B. These sizes do not fit identically because the band length and cup proportions change, but they can be useful when the cup volume seems correct and only the band feels too tight or too loose.

The calculator automatically shows one sister size with a smaller band and one with a larger band in your selected sizing system.

How Should a Bra Fit?

Measurements provide a starting point, but the final test is how the bra actually fits on your body. A well-fitting bra should feel secure without causing painful pressure.

• The band should sit approximately level around the torso instead of riding upward in the back.
• The cups should contain the breast tissue without obvious spilling or large empty areas.
• The straps should stay in place without carrying all of the support.
• The centre gore on many underwire styles should sit close to the chest.
• The underwire should surround the breast tissue rather than resting directly on it.
• You should be able to move, sit, bend, and breathe comfortably.

Common Bra Fit Problems

Bra Band Rides Up in the Back

A band that climbs upward can indicate that the band is too loose, although strap adjustment and bra design can also affect the position. Try a smaller band while moving up one cup step to preserve similar cup volume.

Breast Tissue Spills Over the Cup

Spilling over the top, sides, or centre of the cups often suggests that additional cup space may be needed. Cup shape can also be a factor, so a different style in the same nominal size may fit better.

Cups Gap or Wrinkle

Visible empty space may mean the cup is too large, but it can also mean the cup shape does not match your breast shape. For example, a tall or shallow moulded cup can gap even when the nominal cup volume is close.

Straps Keep Falling Down

Loose straps can sometimes be corrected by adjusting them, but shoulder width, strap placement, band size, and bra style can all contribute. The straps should assist with fit rather than carrying the entire load of the bra.

Straps Dig Into the Shoulders

If the straps are extremely tight because they are being used to create most of the support, check the band fit. A supportive band should reduce the need to overtighten the straps.

Why Bra Size Can Change

A bra size is not necessarily permanent. Body measurements can change with weight changes, pregnancy, hormonal changes, ageing, exercise, medication, or other normal changes in the body.

The bra itself also changes over time. Elastic stretches with repeated wear and washing, which can make an older band feel looser than a new bra labelled with exactly the same size.

Re-measure whenever bras that previously fit well begin feeling noticeably different or when you are buying from an unfamiliar sizing system.

Bra Size in Inches vs. Centimetres

The calculator accepts both inches and centimetres. One inch equals exactly 2.54 centimetres. Switching the measurement unit automatically converts the values already entered into the fields.

You do not need to manually convert your measurements before calculating. Use whichever unit appears on your measuring tape.

Example Bra Size Calculation

Suppose the snug underbust measurement is approximately 32 inches and the full bust measurement is 36 inches. A 32 band is a reasonable measurement-based starting point. The difference between 36 and 32 is four inches.

In a common cup progression, a four-inch difference corresponds to a D cup. The starting size is therefore approximately 32D in U.S., Canadian, and UK sizing. The corresponding band is approximately 70 in EU sizing and 85 in French sizing.

This does not mean every 32D bra will fit the same. A plunge, balconette, full-cup, sports bra, wireless bra, and moulded T-shirt bra can all fit differently even when the label shows the same size.

Bra Size Calculator vs. Brand Size Chart

A general calculator is most useful for finding a starting size. Before ordering a specific product online, compare that result with the manufacturer's own size chart.

Brands can use different cup progressions, band stretch, grading rules, and fit models. Some specialty UK brands use extensive double-letter cup ranges, while U.S. brands may label equivalent volumes differently.

If a manufacturer's chart conflicts with a generic conversion chart, use the manufacturer's information for that specific product and review customer fit notes when available.

How Often Should You Measure Your Bra Size?

There is no universal schedule requiring everyone to measure at a fixed interval. A practical approach is to re-measure when your current bras stop fitting normally, after a noticeable change in body measurements, or before buying from a sizing system you have not used before.

Because different styles fit differently, even a recent measurement does not eliminate the need to assess the actual bra once it is on.

Sports Bra Sizing

Some sports bras use traditional band-and-cup sizing while others use clothing sizes such as XS, S, M, L, or XL. If a sports bra uses standard bra sizing, your normal measured bra size is a useful starting point.

If it uses general clothing sizes, check the manufacturer's chart because a Medium in one product may cover a different range of band and cup combinations than a Medium from another brand.

Bra Sizes Are Not the Same as Clothing Sizes

A bra size such as 34DD cannot be reliably converted into a general shirt size such as Medium or Large. Clothing sizes incorporate the bust, waist, shoulders, garment cut, ease, and brand-specific grading, while a bra size represents a band-and-cup relationship.

For that reason, avoid assuming that a larger cup letter automatically means a particular dress, blouse, or T-shirt size.

Understanding Large Cup Sizes

Cup letters beyond D are often misunderstood because the letters do not progress the same way internationally. A UK FF, U.S. H, and EU H may occupy similar positions in some conversion charts even though the labels look very different.

This is why looking only at the letter can be misleading. Always include the band number and sizing system when comparing sizes.

Why Two Bra Size Calculators May Give Different Answers

Different calculators may use different fitting philosophies. Some use a traditional plus-four method, some map the underbust more directly to the band, some round measurements differently, and some use brand-specific tables.

Cup-size tables also differ. One calculator may use U.S. cup lettering while another uses UK lettering without making that distinction obvious.

This calculator intentionally identifies the sizing system and displays international equivalents so you can see that the same approximate cup volume may use different labels.

Bra Measurement Tips

• Use a flexible tape measure rather than a rigid ruler.
• Keep the tape parallel with the floor.
• Measure the underbust snugly without adding inches manually.
• Measure the bust without crushing the breast tissue.
• Repeat each measurement if the first two readings differ.
• Use the same measurement unit for both values.
• Check the manufacturer's size chart before ordering online.
• Try nearby sister sizes when cup volume feels close but the band does not.
• Remember that cup shape can matter as much as cup volume.

Bra Size Calculator Frequently Asked Questions

Final Thoughts

Finding a bra size starts with accurate measurements, but the number and cup letter are only the beginning. Measure your underbust and full bust carefully, use the calculator to identify a reasonable starting size, and then evaluate the way the actual bra fits.

Pay attention to the band, cups, straps, centre, and underwire rather than relying only on the size printed on the label. When shopping internationally, use the conversion results to compare USA, Canadian, UK, European, and French sizing, and check the individual brand's size chart before ordering.