Bra Size Calculator

Use the Bra Size Calculator to estimate a starting band and cup size from your underbust and fullest bust measurements. Select inches or centimeters and compare US, UK, EU, and Australian labels. The result is a starting point because cup shape, wire width, band stretch, breast shape, and brand grading can change the best fit.

Which Measurements Determine Bra Size?

Underbust and full-bust circumference provide the main starting measurements. Tight and loose underbust measurements can help show how much ribcage compression and band flexibility may feel comfortable.

Bust volume is estimated relative to the selected band. This means a D cup on one band does not have the same volume as a D cup on every other band.

How to Measure Underbust

Stand naturally and wrap a flexible tape directly beneath the breast tissue. Keep the tape parallel to the floor around the front, sides, and back.

For a snug measurement, pull the tape close enough to stay secure without causing pain or changing your breathing.

How to Measure Full Bust

Wrap the tape around the fullest bust circumference. Keep it level and avoid compressing the breast tissue.

Measure without a bra or while wearing a thin, unpadded bra that maintains a natural shape.

Loose, Snug, and Tight Underbust Measurements

A loose underbust is taken with minimal tape tension. A snug underbust is comfortably secure. A tight underbust is pulled firmly around the ribcage without causing pain.

Comparing all three can provide context about ribcage softness and band preference.

How Band Size Is Estimated

Common US and UK band labels usually progress in even numbers such as 30, 32, 34, and 36.

Modern fitting methods frequently begin close to the actual snug underbust rather than automatically adding several inches.

How Cup Size Is Estimated

Cup size is estimated from the difference between full bust and the band reference.

A larger difference generally moves the starting estimate farther through the cup-letter progression.

General Bust-Difference Cup Guide

Cup progressions vary between brands, particularly in US sizing. Always confirm the retailer's chart.

Why Cup Letters Are Relative

A 32D and a 38D do not contain the same approximate cup volume. Cup volume increases as the band increases, even when the cup letter stays the same.

What Are Sister Sizes?

Sister sizes are neighboring band and cup combinations with similar cup volume.

Going down one band generally requires moving up one cup. Going up one band generally requires moving down one cup.

Example Sister Sizes

Letter names depend on the regional system, so compare cup volume rather than letters alone.

US Bra Sizing

US bands are commonly labeled in even inch-based numbers. Cup progressions vary by brand after D and may include DD, DDD, F, G, H, and later letters.

UK Bra Sizing

UK bands use similar inch-based labels, while cup progressions commonly include repeated letters such as DD, FF, GG, HH, and JJ.

EU Bra Sizing

EU band sizes commonly use centimeter-based labels such as 65, 70, 75, and 80.

EU cup progressions are frequently single letters, though brands can differ.

Australian Bra Sizing

Australian band labels commonly use apparel-style numbers such as 8, 10, 12, and 14.

Cup labels often resemble UK progressions, but the exact brand chart should be checked.

General Band Conversion Chart

How the Bra Band Should Fit

The band should stay approximately level around the body and remain secure when the straps are loosened.

A new bra should generally fit on the loosest usable hooks so the tighter hooks remain available as the elastic relaxes.

Signs the Band Is Too Tight

• The band causes pain or severe pressure.
• Normal breathing feels restricted.
• The wires distort or spread unnaturally.
• The closure strains.
• The band creates more discomfort than support.

Signs the Band Is Too Loose

• The back band rides upward.
• The bra shifts during movement.
• The straps carry most of the support.
• The center gore moves away from the body.
• The band closes only on the tightest hooks when new.

How the Cups Should Fit

Breast tissue should sit fully inside the cups without spilling, folding, or being compressed into the wrong area.

The cup edge should follow the body without cutting in or creating major gaps.

Signs the Cups Are Too Small

• Breast tissue spills above or beside the cup.
• The center gore floats away from the sternum in a wired bra.
• The wires rest on breast tissue.
• The cup edge cuts in.
• The cups are pushed downward or outward.

Signs the Cups Are Too Large

• The cup fabric wrinkles or collapses.
• Large gaps appear along the cup edge.
• The cup apex sits away from the fullest point.
• The wires extend far beyond the breast root.
• The cup height interferes with the arm or strap area.

How the Center Gore Should Fit

In many wired everyday bras, the center gore should rest close to the sternum without pressing painfully.

Plunge styles use a lower gore, while some wireless or compression designs behave differently.

How Underwires Should Fit

Underwires should follow the breast root and rest on the ribcage rather than breast tissue.

Wire width and shape can create fit problems even when band and cup volume appear correct.

How Bra Straps Should Fit

Straps should stabilize the cups without digging deeply or carrying all the support.

Frequent strap slipping can come from loose adjustment, narrow shoulders, wide strap placement, or an oversized band.

Breast Shape and Bra Size

Two people with similar measurements can need different bra styles because breast volume can be shallow, projected, full on top, full on bottom, close-set, wide-set, or asymmetrical.

Shallow vs. Projected Breasts

Shallow breasts distribute volume across a wider base. Projected breasts extend farther forward from the chest.

Both can have similar measured volume while requiring different cup shapes.

Full-on-Top vs. Full-on-Bottom Shape

Full-on-top shapes may need open upper cups, while full-on-bottom shapes may fit better in cups with lower depth and controlled upper edges.

Close-Set and Wide-Set Breasts

Center-gore width and wire placement affect whether a bra fits closely set or widely spaced breast roots.

Breast Asymmetry

Mild asymmetry is common. Fit the larger side when possible and adjust the smaller side with strap settings or removable inserts.

T-Shirt Bras

T-shirt bras use smooth, molded cups. Their fixed cup shape can gape or cut in when the breast shape does not match the mold.

Balconette Bras

Balconette bras commonly use wider-set straps and a more open upper cup. Cup height and upper fullness affect fit.

Plunge Bras

Plunge bras use a lower center gore and can suit lower necklines or close-set shapes.

Sports Bras

Sports bras may use compression, encapsulation, or both. Their band, coverage, movement control, and cup system can differ from everyday bras.

Wireless Bras

Wireless bras rely on band construction, fabric, seams, and cup structure rather than an underwire.

What to Do When Between Band Sizes

Compare the firm and relaxed band options. When moving up one band, move down one cup to preserve similar cup volume.

When moving down one band, move up one cup.

What to Do When Between Cup Sizes

Choose the cup that contains all breast tissue without cutting in, collapsing, or placing wires on the breast root.

Trying another cup shape may work better than changing cup volume.

How to Put on and Adjust a Bra

1. Fasten a new bra on the loosest usable hooks.
2. Position the band directly beneath the breast root.
3. Place all breast tissue inside the cups.
4. Check underarm and lower-cup tissue placement.
5. Adjust the straps without overtightening them.
6. Check the band, cups, gore, wires, and movement.

How to Choose Bra Size Online

1. Take current underbust and full-bust measurements.
2. Confirm the regional sizing system.
3. Use the exact product chart.
4. Check whether the band is firm or stretchy.
5. Review cup shape, wire width, and cup height.
6. Read repeated fit comments.
7. Check return and exchange rules.

Why Bras in the Same Size Fit Differently

Bra styles use different cup depth, width, height, seam placement, wire shape, strap position, padding, lining, and band elasticity.

The labeled size should be treated as a starting coordinate rather than a guarantee of identical fit.

When to Remeasure Bra Size

• After noticeable weight change
• During or after pregnancy
• During nursing or weaning
• After breast or chest surgery
• After changes in exercise or muscle development
• When bands consistently ride upward
• When cups repeatedly spill or gape
• When existing bras are stretched or several years old

Common Bra-Sizing Mistakes

• Adding several inches automatically to underbust
• Measuring over a padded or compressive bra
• Pulling the bust tape too tightly
• Assuming cup letters have fixed volume
• Ignoring sister sizes
• Using US and UK cup letters as though they always match
• Choosing a larger band to solve a cup problem
• Choosing a larger cup to solve a loose band
• Ignoring breast shape and wire width
• Expecting every bra in one size to fit identically