How do I measure my bra size at home?

Wear a non-padded bra, wrap a soft tape measure snugly around your ribcage directly under your bust for the band measurement, then measure around the fullest part of your bust for the bust measurement, keeping the tape level and parallel to the floor both times.

What is a band measurement in bra sizing?

The band measurement is taken snugly around your ribcage just under the bust. It determines the number in your bra size, such as the 34 in a 34C, and is meant to provide most of a bra's support.

What is a bust measurement in bra sizing?

The bust measurement is taken around the fullest part of your chest, usually across the nipple line, with the tape level. The difference between this number and your band measurement determines your cup size.

Why do UK and US bra sizes look the same but fit differently?

Band numbers usually match between US and UK sizing, but cup letters diverge above a D cup: the US commonly uses DD/E, DDD/F and G, while the UK continues DD, E, F, FF, G, so the same letter can represent a different actual size in each system.

What are sister sizes?

Sister sizes are different band and cup combinations that share the same overall cup volume. Going up one band size while going down one cup letter, or the reverse, usually keeps a very similar cup fit while changing how snug the band feels.

How do I know if my band size is too big or too small?

A well-fitted band sits level all the way around, doesn't ride up your back, and allows about two fingers to slide underneath comfortably. If it rides up or leaves red marks, the band is too loose or too tight.

How do I know if my cup size is too small?

Spilling over the top or sides of the cup, wrinkling or gapping fabric, or underwire that doesn't sit flat against your ribcage are all signs the cup size needs adjusting.

What does DD/E mean versus the UK's DD?

In US sizing, DD and E are typically used interchangeably for the same cup size. In UK sizing, DD and E are two separate, consecutive cup sizes, so a UK DD is smaller than a UK E.

Should my bra size change after weight loss or gain?

Yes, noticeable weight changes often shift both band and cup measurements, so it's worth re-measuring rather than assuming your old size still fits.

Does pregnancy or breastfeeding change bra size?

Both commonly change band and cup size, sometimes significantly and sometimes day to day, so re-measuring periodically during and after pregnancy or while breastfeeding is recommended.

How often should I re-measure my bra size?

Checking your measurements every six to twelve months, or after any significant weight change, pregnancy, or surgery, helps catch gradual sizing shifts before they become uncomfortable.

Why does bra sizing vary between brands?

There's no single global manufacturing standard for bras, so cup shape, wire width, and band stretch all vary by brand and even by style within the same brand, which is why a calculated size is a strong starting point rather than a guarantee.

Should I measure over or under clothing?

Measure while wearing a thin, non-padded bra rather than bare skin or a padded bra, since a padded or heavily textured bra can distort both the band and bust measurements.

Can I measure my bra size without a tape measure?

A flexible measuring tape gives the most accurate result, but a piece of string measured against a ruler afterward can work as a temporary substitute if a tape measure isn't available.

What's the difference between wired and wireless bras for fit?

Underwire bras use a rigid wire to define and support the cup along the ribcage, which can offer more lift and shaping, while wireless bras rely on fabric and band elasticity, often prioritizing comfort over structured support.

How many hooks should a new bra fasten on?

A new bra should typically fasten comfortably on the loosest hook, leaving room to tighten to the middle and tightest hooks as the band stretches out with wear and washing over time.

What does the band do versus what the cup does?

The band is responsible for roughly 80 percent of a bra's support and should feel snug on its own, while the cup exists mainly to contain and shape the bust rather than to hold up most of the weight.

Is a bigger cup size always uncomfortable?

Not necessarily — discomfort usually comes from an incorrect band or cup combination rather than cup size itself, since a properly matched band and cup can feel comfortable at almost any size.

How do I convert my US bra size to EU, UK, FR, IT or AU sizes?

Band numbers convert using regional formulas (for example, EU band sizes run in 5cm steps different from US/UK inch-based steps), while cup letters shift slightly between regions above a D cup; a calculator that applies these regional formulas removes the need to do the conversion by hand.

What should I do if I'm between two sizes?

Try both sizes if possible, since brand and style differences mean one will usually fit better in practice; as a general rule, sizing down on the band and up on the cup tends to give a snugger, more supportive fit than the reverse.

Bra Size Calculator - RKfashionzone

Enter your measurements

Two quick measurements are all it takes to get your size, sister sizes, and international conversions.

Band Measurement (in) Snug measurement directly under your bust.

Bust Measurement (in) Around the fullest part of your bust.

Band: Wearing a non-padded bra, wrap the tape snugly around your ribcage right under your bust, keeping it level and parallel to the floor.
Bust: Wrap the tape around the fullest part of your bust, usually across the nipple line, without pulling it tight.
Round both measurements to the nearest whole number, then enter them above.

Results are a strong starting estimate — fit still varies by brand and style.

Your recommended size

US Size

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Bra size charts & comparisons

Visualize how cup sizes progress and how the same size looks across different countries.

Cup Size Progression (Bust − Band, in inches)

Band Size by Country (for a US 34)

Bust measurement (in inches) needed for each band and cup combination, based on the standard sizing formula used by this calculator.
Band	AA	A	B	C	D	DD/E	DDD/F	G	H
28	24″	25″	26″	27″	28″	29″	30″	31″	32″
30	26″	27″	28″	29″	30″	31″	32″	33″	34″
32	28″	29″	30″	31″	32″	33″	34″	35″	36″
34	30″	31″	32″	33″	34″	35″	36″	37″	38″
36	32″	33″	34″	35″	36″	37″	38″	39″	40″
38	34″	35″	36″	37″	38″	39″	40″	41″	42″
40	36″	37″	38″	39″	40″	41″	42″	43″	44″
42	38″	39″	40″	41″	42″	43″	44″	45″	46″
44	40″	41″	42″	43″	44″	45″	46″	47″	48″

Understanding bra sizing

The background behind the numbers, so you know exactly what your size means.

How bra sizing actually works

A bra size is really two separate measurements combined into one label: a band number describing your ribcage circumference, and a cup letter describing how much larger your bust is than that band. Because the band carries most of the support, getting it right matters just as much as the cup — a bra with a loose band and a “correct” cup letter will still feel unsupportive, since the cup was designed to work with a snug band underneath it.

Why bra sizes aren’t standardized worldwide

Unlike shoe sizing, there’s no single international body that regulates bra measurements, so each region developed its own numbering system independently. The US and UK largely share the same band numbers but diverge on cup letters past a D cup, while continental Europe, France, and Italy each use entirely different band numbering based on centimeters rather than inches. That’s why the exact same physical bra can be labeled a 34C, a 75C, and an FR 90C depending on where it’s sold — they describe the same fit, just counted differently.

Common bra fitting mistakes

Wearing the band too loose. A stretched-out or oversized band shifts all the support onto the shoulder straps, which is a common cause of shoulder discomfort.
Assuming cup size is fixed. A cup letter only means something relative to its band — a 32D and a 36D hold noticeably different volumes, even though both are “D cups.”
Sticking to one brand’s size forever. Cut, wire shape, and fabric stretch vary enough between brands that your size can genuinely shift when you switch labels.
Never re-measuring. Weight changes, hormonal changes, and even how worn-out an old bra’s elastic is can all quietly shift what actually fits well.

Signs you’re wearing the wrong size

A band that rides up at the back, straps that dig in or constantly slip, cups that gap or spill over, and an underwire that doesn’t sit flat against your ribcage are the most common tells that your current size no longer matches your body. If more than one of these sounds familiar, it’s worth re-measuring with the calculator above and comparing the result — including its sister sizes — against what you’re currently wearing.

Get an even better fit

A few extra pointers to make sure your calculated size actually feels right on.

The two-finger band test

A properly fitted band should let you slide two fingers underneath comfortably, sitting level all the way around without riding up your back.

Start on the loosest hook

A new bra should fasten comfortably on the loosest set of hooks, leaving room to tighten as the band stretches with wear and washing.

Try your sister sizes

If the calculated size feels slightly off, its sister sizes usually have a near-identical cup volume with a different band feel — worth trying both.

Re-measure regularly

Weight changes, pregnancy, and even the style of bra you’re used to wearing can shift your true size, so re-check every six to twelve months.

Frequently asked questions

Everything you need to know about measuring, sister sizes, and international conversions.

More fit and style guides from around the site.

Bra Size Calculator

Enter your measurements

Your recommended size

Bra size charts & comparisons

Cup Size Progression (Bust − Band, in inches)

Band Size by Country (for a US 34)

Understanding bra sizing

How bra sizing actually works

Why bra sizes aren’t standardized worldwide

Common bra fitting mistakes

Signs you’re wearing the wrong size

Get an even better fit

The two-finger band test

Start on the loosest hook

Try your sister sizes

Re-measure regularly

Frequently asked questions

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