Bra Size Calculator

This page holds two tools. The first turns a bust and a band measurement into a size in every major system at once. The second converts a size you already know from one system to another. A 95 cm bust over an 85 cm band comes out as 34C in the US and Canada, 34C or dress code 10 in the UK, 75E under EN 13402, 90E in France, Belgium and Spain, and dress code 12 in Australia and New Zealand.

Taking the two measurements

Everything downstream depends on getting these two numbers right, and they are measured differently on purpose.

The bust is a loose circumference, taken around the chest over the fullest part of the breasts, standing straight with the arms at the sides, while wearing a bra that already fits reasonably well. Loose means the tape rests on the body without compressing anything.

The band, sometimes called the frame, is a firm circumference taken directly underneath the breasts. Firm means snug but not tight: the tape should sit level all the way round, parallel to the floor, and it should not dig in. Letting it ride up at the back is the most common measuring error, and it inflates the number.

Take both measurements twice. If the two attempts disagree by more than about half an inch, take them again, because half an inch is enough to move the cup letter.

Incorrect bra fit

Surveys and articles regularly claim that somewhere between 70 and 85 percent of women wear the wrong bra size. The methods behind those figures are not consistent between sources and the percentages may be inflated, but poor fit is a real and well-documented problem, judging by the volume of studies, articles and complaints about the lack of size standardisation.

Studies looking at what people actually pick have found the same pattern repeatedly: the most common mistake is choosing a band that is too large and a cup that is too small. Part of the problem is that band and cup sizes are not standardised. They vary between countries and between manufacturers, which makes any published size an approximation rather than a specification. A 34B from two different companies may not fit the same person, and neither one is wrong.

Signs of a bra that does not fit include the band digging into the torso or riding up the back, red marks, shoulder or neck pain, breast tissue overflowing around the edges of the cups, and the centre panel between the cups not lying flat against the sternum. That last one is the quickest single check: if the centre panel floats away from the body, the cup is usually too small.

Band size, or frame size

The band is the part of the bra that goes around the torso, and it does most of the work. On a well-fitting bra the band carries the great majority of the support and the straps carry very little, which is why a band that is too loose cannot be fixed by tightening the straps. It only transfers the load to the shoulders, which is where the aching comes from.

Band sizes are quoted in different measurements in different countries, so a small, a medium and a large mean different numbers depending on where the bra was made. The table below lines them up.

Band size	FR/BE/ES	EU (EN 13402)	US and UK	AU, NZ
XXS	75	60	28	6
XS	80	65	30	8
S	85	70	32	10
M	90	75	34	12
L	95	80	36	14
XL	100	85	38	16
XXL	105	90	40	18
3XL	110	95	42	20
4XL	115	100	44	22
5XL	120	105	46	24

Every system steps in the same increments, which is why band conversion is arithmetic rather than a lookup: two inches in the US and UK, five centimetres in continental Europe, and two dress sizes in Australia and New Zealand. That is exactly what the converter above does.

Cup size

The cup is worked out from the difference between the bust and the band, not from either number on its own. In the US and UK the difference is read in inches, and roughly each inch is one cup letter.

Bust minus band, inches	US cup	UK / AU cup
under 1	AA	AA
1	A	A
2	B	B
3	C	C
4	D	D
5	DD/E	DD
6	DDD/F	E
7	DDDD/G	F
8	H	FF
9	I	G
10	J	GG
11	K	H
12	L	HH
13	M	J
14	N	JJ

The two ladders agree up to D and then split. A US DD and a UK DD are the same, but a US DDD is a UK E, a US DDDD is a UK F, and the gap widens from there. This is the single most common source of confusion when buying from abroad, and it is why the converter reports cup letters separately for each system rather than passing the same letter through.

Continental Europe works from the difference in centimetres instead, and against the EU band number rather than the raw measurement.

Bust minus band, cm	Continental Europe cup
10 to 11	AA
12 to 13	A
14 to 15	B
16 to 17	C
18 to 19	D
20 to 21	E
22 to 23	F
24 to 25	G
26 to 27	H
28 to 29	I
30 to 31	J
32 to 33	K

That is why the same measurements can read as a C in the US and an E in Europe without anything being wrong. The letters belong to different scales.

Sister sizes

Cup volume depends on both letters and numbers together. Keeping the same letter while changing the band changes the actual size of the cup, because the letter describes a difference rather than a volume.

Sister sizes are the sizes that hold roughly the same volume with a different band. Going down a band means going up a cup letter, and going up a band means going down one. A 34C has sisters at 32D and 36B. All three hold a similar amount; they differ in how tight the band is.

This is the practical fix when a bra is close but not right. If the cups fit and the band rides up, try the next band down with the next cup letter up. If the band is comfortable and the cups overflow, stay on the band and go up a letter instead. The calculator lists both sisters alongside the main result.

The underbust +4 method

Older fitting guides told people to measure the underbust and add four inches, or five if the number came out odd. The calculator reports those sizes too, greyed out, because a few manufacturers still use them.

The method dates from a period when bra fabrics had far less stretch than modern ones, and the extra inches were an allowance for that. With today's elastics the addition usually produces a band several inches too loose, and because the cup is calculated from the same difference, a bigger band number silently shrinks the cup. That is precisely the too-big-band, too-small-cup pattern the fit studies keep finding. Use the plain measurement unless a specific brand tells you otherwise, and treat the +4 rows as a translation for older size charts rather than a recommendation.

Checking the fit once the bra is on

A calculated size is a starting point for trying things on, not an answer. Once a bra is on, four checks settle it quickly.

The band should sit level all the way round, not riding up at the back, and two fingers should slide under it with mild resistance. Fasten a new bra on the loosest hook, so there is somewhere to go as the elastic relaxes over the months. The centre panel should lie flat against the sternum. And the cups should contain the tissue without gaps at the top or spillage at the sides or under the arms, which is easier to judge after leaning forward and settling everything into the cups.

Sizes move. Weight change, the menstrual cycle, pregnancy, breastfeeding and simple ageing all shift the measurements, and elastic wears out with washing and wear. Remeasuring once a year, and again after any noticeable weight change, is a reasonable habit.

Reading the results on this page

The first panel leads with the US and Canadian size and lists the equivalent in each other system underneath, along with the bust-minus-band difference both calculations run on and the two sister sizes. The table below it reproduces every system in full, with the underbust +4 rows dimmed to mark them as the older method. The converter is for when you already know one size and need the others, which is the usual case when ordering from a shop in another country.