What size is a 34 inch underbust and a 38 inch bust?

That is a 34D in US sizing. The underbust of 34 inches is already even, so the band is 34. The bust of 38 inches minus the band of 34 leaves a 4 inch difference, and 4 inches is a D cup. The same size is a 34D in the UK, a 75D in continental Europe, a 90D in France, a 12D in Australia and a 75D in Japan. Its sister sizes are 32DD and 36C.

Should I add four inches to my underbust measurement?

Not if you are following the method most fitters and most current brand guides use. The legacy US rule added 4 inches to an even underbust measurement and 5 to an odd one, a convention from an era of far less elastic fabric. Modern band rules round the raw underbust measurement to the nearest even inch instead, which produces a band roughly four inches smaller and a correspondingly larger cup letter. Both rules are supported in the calculator above so you can see what each produces from the same tape readings; a 31 inch underbust with a 37 inch bust returns 32DD under the modern rule and 36A under the legacy one.

What are sister sizes?

Sister sizes are labels that share the same cup volume on a different band. Going down one band adds one cup letter and going up one band removes one, so 30DD, 32D, 34C, 36B and 38A are all cut with the same cup. They matter for two reasons: they let you keep the cup you need when a band runs tight or loose in a particular style, and they explain why a C cup is not one fixed size — a 30C and a 38C hold noticeably different volumes.

What is a US 34C in UK and European sizes?

A US 34C is a 34C in the UK, a 75C in continental Europe, a 90C in France, Belgium and Spain, a 12C in Australia and New Zealand, and a 75C in Japan. The band converts arithmetically: the European number is the underbust in centimetres rounded to a 5 cm step, France adds 15 to the European number, and Australia uses the dress-size band, which is the US number minus 22. Cup letters only diverge from the fifth step upward, where the US uses DD, the UK also uses DD and Europe switches to E.

Is a DD bigger than a D?

Yes, by one cup step, which is one inch of difference between the bust and band measurements at the same band number. A 34DD is cut for a 39 inch bust where a 34D is cut for a 38 inch bust. Above DD the US progression continues DDD, G, H, I, J. The UK progression runs DD, E, F, FF, G, GG instead, so a US DDD is a UK E, and continental Europe simply carries on through the alphabet, where the same cup is an F.

Why does the same size fit differently in different brands?

There is no legal standard for bra sizing in the United States or the United Kingdom, so each brand grades its own patterns. Cup depth, wire width, strap placement and how much the band stretches under load all vary, and the same label can be cut to different measurements from one label to the next. The European standard EN 13402 defines how a garment should be labelled but does not force one grading rule on manufacturers. Treat a calculated size as the starting point, then use the fit checks on this page and the sister sizes to adjust.

How often should I re-measure?

Re-measure once a year as routine, and any time the fit changes. Band elastic relaxes with wear and washing, so a band that fitted on the loosest hook when new will eventually not hold on the tightest one — that is the point at which the garment is worn out, not a sign that the size changed. Also re-measure after any change in body weight, during and after pregnancy, and after any surgery affecting the chest, since the underbust measurement is what moves first.

Health

Bra Size Calculator

The band comes from the underbust measurement and the cup from bust minus band, at one inch of difference per cup step. Enter both measurements in inches or centimetres for the US size, the sister sizes, and the UK, EU, FR, AU and Japan equivalents — with either band rounding rule.

Your measurements

Underbust measurement

Snug around the ribcage, directly under the bust

Bust measurement

Loose around the fullest point of the bust

Band rule

The modern method, used by most fitters and by brands that publish a measuring guide today.

Your size

32DD

band 32 · cup DD · difference 5 in

Cup step (inches of difference)

DDD

Sister sizes (same cup volume)

one band down, one cup up

30DDD

one band up, one cup down

34D

The same size elsewhere

32DD

70E

85E

10DD

70E

Add 4 / 5 in gives

36A

Measured in cm

78.7 / 94

Try a pair of measurements

Band 32 comes from the underbust; the cup comes from 37 − 32 = 5 in of difference. The band rule you pick moves the answer, so both are shown.

No sign-up · Free

The basics

What a bra size actually measures

A bra size is two independent dimensions printed as one label: a number and a letter. The number is a circumference and the letter is a difference between two circumferences. They are read from two tape measurements, and nothing else about the label carries any information.

band = underbust, rounded

The number is the band

The band is the circumference of the ribcage directly under the bust. It is the part of the garment that carries the load, which is why it is the measurement worth getting right first. Band numbers are always even, so the raw measurement u is rounded to the nearest even inch.

Underbust 31 in → band 32

cup step = bust − band

The letter is a difference

The cup letter encodes how much larger the bust circumference b is than the band, not an absolute size. One whole inch of difference is one cup step. Because the difference is measured from the band, the same letter on a different band number is a different volume.

Bust 37 in − band 32 in = 5 in → cup DD

Method

How to work out the size by hand

Four steps take you from two tape readings to a label. Everything the calculator does is in these four lines.

1
Measure the underbust and round it to an even number
Take the underbust circumference u in inches and round it to the nearest even inch. That is the band. If your tape reads in centimetres, divide by 2.54 first, because the cup step is defined in inches.
31 in → band 32
2
Measure the bust at its fullest point
Take the bust circumference b with no tension on the tape. This is the only other number the calculation needs.
b = 37 in
3
Subtract the band from the bust
The difference d is what selects the cup. Round it to the nearest whole inch; a half inch either way is inside the tolerance of the measurement itself.
d = 37 − 32 = 5 in
4
Read the cup letter off the progression
Count one cup step per inch of difference: AA, A, B, C, D, DD, DDD, G, H and on up. Write the band and the letter together.
5 in → DD · size 32DD

Taking the measurements

How to measure correctly with a tape

The arithmetic is trivial; the measurement is where the error lives. A tape that rides up at the back, or is pulled tight on the bust reading, moves the answer by a full cup step or more. Work through these in order, and take each reading twice.

1
Wear an unpadded bra, or nothing on top
Padding, moulded foam and sports compression all change the bust measurement — some add an inch, some remove one. A thin unlined bra that still fastens is the reference garment; bare is equally fine.
no padding, no compression
2
Measure the underbust, snug and level
Bring the tape around the ribcage directly beneath the bust, keep it parallel to the floor all the way round, and pull it firm enough that it does not slide down but not so tight that it compresses the ribs. Breathe out and read the number.
underbust → the band
3
Measure the bust at its fullest point
Stand upright with arms relaxed at your sides. Take the tape around the fullest point of the bust with no tension at all — the tape should touch but not press. Keep it level front and back; a tape that rides up at the back reads short.
bust → the cup
4
Record both numbers to the nearest half inch
Half an inch is the useful precision here: it is enough to settle which even band you round to, and finer than that is lost in the tape tension anyway. Take each measurement twice and use the repeatable figure.
nearest ½ in (1 cm)
5
Subtract, then read the letter
Round the underbust to the nearest even inch for the band, subtract that band from the bust measurement, and count one cup step per whole inch of difference.
cup step = bust − band

tape tension

Two different tensions

The underbust reading is taken firm, because the band is meant to sit firm. The bust reading is taken with none, because any tension compresses the measurement and returns a cup step too small.

level all the way round

Check the back

A tape that slips up at the back reads short on both measurements. In front of a mirror or with a second person, confirm the tape is parallel to the floor behind you.

no soft tape?

Use a string and a ruler

Wrap a non-stretch string or a strip of paper, mark where it meets, then lay it flat against a ruler. Anything elastic will read long under tension.

Worked examples

The same procedure across five measurement pairs

Odd underbust readings, half inches, and metric input all handle slightly differently. Switch tabs to follow the working and the answer for each.

Given underbust = 31 in, bust = 37 in

Band (round to even): 31 in → 32

Difference: 37 in − 32 in = 5 in

Cup (1 in per step): 5 in → DD (also written E)

Legacy +4/+5 band for comparison: 36 → 36A

32DD (US)

UK 32DD · EU 70E · FR 85E · AU 10DD · JP 70E

Sister down: 30DDDSister up: 34D

The clearest case for checking both band methods: the same tape readings produce two labels four inches apart.

The two band rules

Round to even, or add four inches?

Two rules for turning an underbust measurement into a band number are still in circulation, and they disagree by about four inches. This is the single biggest reason two size calculators hand you different answers from identical measurements, so it is worth knowing which one a chart is using before you trust it.

band = underbust rounded to the nearest even number

Round to the nearest even inch

The modern method, used by most fitters and by brands that publish a measuring guide today.

Underbust 31 in, bust 37 in → 32DD

band = underbust + 4 if even, + 5 if odd

Add four or five inches

The legacy US department-store method. Still printed on some packaging and still used by some older size charts.

Underbust 31 in, bust 37 in → 36A

Note what happens to the cup letter. The band moves by four inches, so the difference moves by four inches in the opposite direction and the cup letter moves four steps with it. The two labels are not close together: from the same tape readings the modern rule returns 32DD and the legacy rule returns 36A.

Underbust	Band, round to even	Band, add 4 or 5	Gap
26 in	28	30	2 in
27 in	28	32	4 in
28 in	28	32	4 in
29 in	30	34	4 in
30 in	30	34	4 in
31 in	32	36	4 in
32 in	32	36	4 in
33 in	34	38	4 in
34 in	34	38	4 in
35 in	36	40	4 in
36 in	36	40	4 in
37 in	38	42	4 in
38 in	38	42	4 in
39 in	40	44	4 in
40 in	40	44	4 in

The gap is four inches on an even underbust and five on an odd one, before the floor at band 28 compresses it.

Sister sizes

Why 34C and 32D hold the same cup

Sister sizes are labels graded to the same cup volume on different bands. The published grading rule is one cup letter per two inches of band: drop the band by one size and add a cup letter, or raise the band by one size and remove one. They are the first thing to reach for when the cup is right but the band is not.

Size	Band	Cup	Relationship to 34C
30DD	30	DD	2 band sizes down, 2 cup steps up
32D	32	D	1 band size down, 1 cup step up
34C	34	C	the reference size
36B	36	B	1 band size up, 1 cup step down
38A	38	A	2 band sizes up, 2 cup steps down

same cup, different band

What a sister size fixes

If the cup fits and the band does not sit firm, take the sister size down: a smaller band with the next cup letter up. If the cup fits and the band is tight, take the sister size up. Changing the band alone changes the cup volume too, which is what people miss.

the arithmetic does not match

Why the numbers look inconsistent

A two-inch band change moves the bust-minus-band difference by two inches but only one cup letter. That is not an error: the cup is graded by both the band and the letter, so a cup letter is a relative step, not a fixed volume. It is also why the calculator lists sister sizes separately rather than recomputing them from the tape.

The scale

The cup progression, inch by inch

One whole inch of difference between the bust and band measurements is one cup step. Where the systems part company is what the steps are called: the US inserts DD and DDD, the UK doubles letters and skips I, and continental Europe simply runs through the alphabet.

Difference	US	UK / AU	EU / FR / JP
0 in (0 cm)	AA	AA	AA
1 in (2.5 cm)	A	A	A
2 in (5.1 cm)	B	B	B
3 in (7.6 cm)	C	C	C
4 in (10.2 cm)	D	D	D
5 in (12.7 cm)	DDalso sold as E	DD	E
6 in (15.2 cm)	DDDalso sold as F	E	F
7 in (17.8 cm)	G	F	G
8 in (20.3 cm)	H	FF	H
9 in (22.9 cm)	I	G	I
10 in (25.4 cm)	J	GG	J
11 in (27.9 cm)	K	H	K
12 in (30.5 cm)	L	HH	L
13 in (33 cm)	M	J	M
14 in (35.6 cm)	N	JJ	N
15 in (38.1 cm)	O	K	O

Conversion

US, UK, EU, FR, AU and Japan side by side

The band converts arithmetically. Continental Europe labels the band as the underbust in centimetres rounded to a 5 cm step; France, Belgium and Spain add 15 to that number; Australia and New Zealand use the dress-size band, which is the US number minus 22; Japan uses the same 5 cm ladder as continental Europe. Cup letters follow the progression in the table above.

Band numbers across systems

Underbust	US	UK	EU	FR	AU	JP
about 27 to 29 in	28	28	60	75	6	60
about 29 to 31 in	30	30	65	80	8	65
about 31 to 33 in	32	32	70	85	10	70
about 33 to 35 in	34	34	75	90	12	75
about 35 to 37 in	36	36	80	95	14	80
about 37 to 39 in	38	38	85	100	16	85
about 39 to 41 in	40	40	90	105	18	90
about 41 to 43 in	42	42	95	110	20	95
about 43 to 45 in	44	44	100	115	22	100
about 45 to 47 in	46	46	105	120	24	105
about 47 to 49 in	48	48	110	125	26	110

Full sizes across systems

The sizes stocked most widely on a US rail, converted in full. Every row is generated from the same rules the calculator uses.

US	UK	EU	FR	AU	JP	Difference
30A	30A	65A	80A	8A	65A	1 in
30B	30B	65B	80B	8B	65B	2 in
30C	30C	65C	80C	8C	65C	3 in
32A	32A	70A	85A	10A	70A	1 in
32B	32B	70B	85B	10B	70B	2 in
32C	32C	70C	85C	10C	70C	3 in
32D	32D	70D	85D	10D	70D	4 in
32DD	32DD	70E	85E	10DD	70E	5 in
34B	34B	75B	90B	12B	75B	2 in
34C	34C	75C	90C	12C	75C	3 in
34D	34D	75D	90D	12D	75D	4 in
34DD	34DD	75E	90E	12DD	75E	5 in
34DDD	34E	75F	90F	12E	75F	6 in
36B	36B	80B	95B	14B	80B	2 in
36C	36C	80C	95C	14C	80C	3 in
36D	36D	80D	95D	14D	80D	4 in
36DD	36DD	80E	95E	14DD	80E	5 in
36DDD	36E	80F	95F	14E	80F	6 in
38C	38C	85C	100C	16C	85C	3 in
38D	38D	85D	100D	16D	85D	4 in
38DD	38DD	85E	100E	16DD	85E	5 in
38DDD	38E	85F	100F	16E	85F	6 in
38G	38F	85G	100G	16F	85G	7 in
40C	40C	90C	105C	18C	90C	3 in
40D	40D	90D	105D	18D	90D	4 in
40DD	40DD	90E	105E	18DD	90E	5 in
40DDD	40E	90F	105F	18E	90F	6 in
42D	42D	95D	110D	20D	95D	4 in
42DD	42DD	95E	110E	20DD	95E	5 in
44D	44D	100D	115D	22D	100D	4 in
44DD	44DD	100E	115E	22DD	100E	5 in
46DD	46DD	105E	120E	24DD	105E	5 in

Quick chart

Size by underbust and bust measurement

Find your underbust measurement down the left, your bust measurement across the top, and read the size where they meet. Switch the band rule or the sizing system to see the same grid in another convention. This is the answer to hundreds of measurement-pair questions without opening the calculator.

Band rule

Sizing system

Bra size by underbust and bust measurement in inches
Underbust ↓ / Bust →	30	31	32	33	34	35	36	37	38	39	40	41	42	43	44	45	46	47	48	49	50
26 inband 28	28B	28C	28D	28DD	28DDD	28G	28H	28I	28J	28K	28L	28M	28N	28O	—	—	—	—	—	—	—
27 inband 28	28B	28C	28D	28DD	28DDD	28G	28H	28I	28J	28K	28L	28M	28N	28O	—	—	—	—	—	—	—
28 inband 28	28B	28C	28D	28DD	28DDD	28G	28H	28I	28J	28K	28L	28M	28N	28O	—	—	—	—	—	—	—
29 inband 30	30AA	30A	30B	30C	30D	30DD	30DDD	30G	30H	30I	30J	30K	30L	30M	30N	30O	—	—	—	—	—
30 inband 30	30AA	30A	30B	30C	30D	30DD	30DDD	30G	30H	30I	30J	30K	30L	30M	30N	30O	—	—	—	—	—
31 inband 32	—	—	32AA	32A	32B	32C	32D	32DD	32DDD	32G	32H	32I	32J	32K	32L	32M	32N	32O	—	—	—
32 inband 32	—	—	32AA	32A	32B	32C	32D	32DD	32DDD	32G	32H	32I	32J	32K	32L	32M	32N	32O	—	—	—
33 inband 34	—	—	—	—	34AA	34A	34B	34C	34D	34DD	34DDD	34G	34H	34I	34J	34K	34L	34M	34N	34O	—
34 inband 34	—	—	—	—	34AA	34A	34B	34C	34D	34DD	34DDD	34G	34H	34I	34J	34K	34L	34M	34N	34O	—
35 inband 36	—	—	—	—	—	—	36AA	36A	36B	36C	36D	36DD	36DDD	36G	36H	36I	36J	36K	36L	36M	36N
36 inband 36	—	—	—	—	—	—	36AA	36A	36B	36C	36D	36DD	36DDD	36G	36H	36I	36J	36K	36L	36M	36N
37 inband 38	—	—	—	—	—	—	—	—	38AA	38A	38B	38C	38D	38DD	38DDD	38G	38H	38I	38J	38K	38L
38 inband 38	—	—	—	—	—	—	—	—	38AA	38A	38B	38C	38D	38DD	38DDD	38G	38H	38I	38J	38K	38L
39 inband 40	—	—	—	—	—	—	—	—	—	—	40AA	40A	40B	40C	40D	40DD	40DDD	40G	40H	40I	40J
40 inband 40	—	—	—	—	—	—	—	—	—	—	40AA	40A	40B	40C	40D	40DD	40DDD	40G	40H	40I	40J
41 inband 42	—	—	—	—	—	—	—	—	—	—	—	—	42AA	42A	42B	42C	42D	42DD	42DDD	42G	42H
42 inband 42	—	—	—	—	—	—	—	—	—	—	—	—	42AA	42A	42B	42C	42D	42DD	42DDD	42G	42H
43 inband 44	—	—	—	—	—	—	—	—	—	—	—	—	—	—	44AA	44A	44B	44C	44D	44DD	44DDD
44 inband 44	—	—	—	—	—	—	—	—	—	—	—	—	—	—	44AA	44A	44B	44C	44D	44DD	44DDD
45 inband 46	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	46AA	46A	46B	46C	46D
46 inband 46	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	—	46AA	46A	46B	46C	46D

Rows are the underbust measurement in inches, columns the bust measurement in inches. A dash means the bust measurement is smaller than the band number, or further above it than the graded range covers — re-check the tape if a real pair of measurements lands there.

Fit diagnostics

What a poor fit tells you about the size

A calculated size is a starting point. What the garment does when worn is the real measurement, and each symptom points at a specific dimension: the band, the cup volume, or the strap length. Work down the band first — almost everything else follows from it.

What the garment does	What it indicates	Adjustment
The band rides up at the back	The band is too large, so it is not anchored and the weight has transferred to the straps.	Go down one band and up one cup — the sister size down — before changing anything else.
The straps slip off the shoulders	Usually the same loose band, occasionally a strap set wider apart than your shoulders.	Shorten the straps first. If they still slip at their shortest, the band is the real problem.
The straps dig in and leave marks	The band is carrying too little of the load. A correctly fitted band takes most of the weight.	Tighten the band by a size, or move to a tighter hook, and lengthen the straps.
The cup gapes or wrinkles at the top edge	The cup is larger than the volume it holds, or the cut is a fuller shape than the garment needs.	Drop one cup step at the same band, or try a style with less depth at the top of the cup.
The cup overflows at the top or the underarm	The cup volume is too small for the bust measurement at that band.	Go up one cup step at the same band. If the band is also tight, take the sister size up instead.
The underwire sits on the bust rather than the ribcage	The wire is too narrow or too shallow for the cup — a cup volume that is too small, or a wire shape that does not match.	Go up a cup step, or try a brand whose wire is cut wider at the same size.
The centre panel does not lie flat against the sternum	Cup volume too small, or a wire width that does not match, so the panel is held off the body.	Go up one cup step at the same band and re-check. A flat centre panel is the single clearest fit check.
The band is comfortable only on the tightest hook when new	The band is too large. New elastic should fit on the loosest hook so the tighter hooks remain available as it relaxes.	Go down one band size and up one cup step.

Why labels disagree

Why the same size differs between brands and countries

Two garments labelled 34D can be cut to measurably different dimensions. That is not a fault in the arithmetic on this page; it is what happens when a label is not tied to a standard.

no legal standard

Nobody defines the label

Neither the US nor the UK has a mandatory sizing standard for this garment. The European standard EN 13402 sets out how a garment should be labelled and which body measurements the label refers to, but it does not force one grading rule on manufacturers.

grading varies

Pattern grading is a house rule

Every brand decides how much cup depth, wire width and strap position change per size step. Two labels can agree on the band and still cut cups that differ by a step in practice, which is why a size that works in one range needs checking in another.

band stretch

Elastic content moves the fit

Bands are made of stretch fabric, and how much stretch a brand builds in changes how a given band number wears. A firmer band at the same number behaves like a smaller one.

vanity sizing

Labels drift over time

Where labels compete on the number rather than the measurement, the measurement behind a given label tends to drift upward over the years. Compare published measurement charts rather than labels when moving between brands.

Where it shows up

When the two numbers matter

Three situations account for almost every visit to a size calculator.

ordering online

No fitting room

With nothing to try on, the tape and the size chart are the only inputs you have. Order your calculated size and both sister sizes where returns are free, then keep the one that passes the fit checks.

crossing systems

Buying from another country

A UK, French or Japanese label is a different notation for the same two dimensions. Convert the size rather than guessing, and check the brand chart in centimetres where one is published.

replacing a worn garment

The band has relaxed

When a band only holds on the tightest hook, the elastic is spent rather than the size being wrong. Re-measure before replacing, since the underbust is the number most likely to have moved.

Worth knowing

Rules worth remembering

Six things that decide whether the calculated size is the one that works, none of which appear on the label.

the band carries the load

Fit the band first

A band that does not stay level does not support anything, and every other symptom follows from it. Get the band right, then adjust the cup with the sister size.

new on the loosest hook

Hooks are a wear allowance

A new band should fasten comfortably on the loosest hook so the tighter ones stay available as the elastic relaxes. Buying a band that already needs the tightest hook leaves no allowance at all.

a letter is a step, not a size

C is not one volume

The cup letter is a difference from the band, so a 30C and a 38C are not the same volume. Comparing letters across band numbers is meaningless.

re-measure yearly

The underbust moves first

Re-measure once a year and after any change in body weight, pregnancy, or surgery affecting the chest. The band number changes before the cup letter does.

wash cool, dry flat

Care is a sizing question

Heat is what destroys the elastane in a band. Washing cool and drying flat, and rotating between several garments so each rests a day, keeps a band at its measured size far longer.

brand charts beat labels

Measure the garment, not the letter

Where a brand publishes the body measurements behind each size, use those and ignore the letter. Two charts that disagree are usually using the two different band rules.

Glossary

The terms on a size chart

Size charts use a small, specific vocabulary, and most of the confusion online comes from two charts using the same word for different measurements.

Underbust measurement: The circumference of the ribcage directly under the bust, taken firm and level. Sometimes labelled the rib or frame measurement. It sets the band.
Band size: The even number on the label. Under the modern rule it is the underbust rounded to the nearest even inch; under the legacy rule it is that measurement plus four or five.
Bust measurement: The circumference around the fullest point of the bust, taken with no tension on the tape. Also called the over-bust measurement.
Cup difference: The bust measurement minus the band number, in inches. One whole inch is one cup step. This is the only thing the cup letter encodes.
Sister size: A label with the same graded cup volume on a different band: one band down and one cup letter up, or one band up and one cup letter down.
Centre gore: The panel between the two cups. Whether it lies flat against the sternum is the quickest single check that the cup volume is right.
Grading: How a brand scales a pattern from one size to the next. Because grading is not standardised, two garments with the same label can differ measurably.
EN 13402: The European standard for size labelling of clothes. It defines the body measurements a label refers to and how they are printed, not the cut of the garment.

FAQ

Common questions

Take two measurements with a tape. First the underbust: snug around the ribcage directly beneath the bust, level all the way round. Second the bust: loose around the fullest point, with the tape touching but not pressing. Round the underbust to the nearest even inch and that is your band number. Subtract the band from the bust measurement and count one cup step per whole inch of difference: 0 inches is AA, 1 is A, 2 is B, 3 is C, 4 is D, 5 is DD, 6 is DDD, then G, H, I and on. A 31 inch underbust with a 37 inch bust gives a band of 32 and a difference of 5 inches, so 32DD.

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