Bra Size Calculator: How to Measure Bra Size
Two measurements. Your band and cup in US, UK, EU, FR and AU, your sister sizes, and every bra we stock in that size. About thirty seconds, then the full guide to measuring at home below.
How to measure bra size, in two sentences Measure snug around your ribcage directly under the bust and round to the nearest even inch: that is your band. Measure loosely across the fullest part of your bust, subtract the band, and every inch of difference is one cup letter, starting at A. A 34″ underbust and a 37″ bust is a 34C.
Not sure where the tape goes? See the diagrams below
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What you need to measure your bra size at home
Four things, two minutes. Most fit problems trace back to the band rather than the cup, and getting the band measurement right takes less time than reading the rest of this page.
A soft tape measure, or a substitute
Fabric or vinyl, the kind that bends. A metal builder's tape will not sit flat and reads long. No tape? A ribbon, phone cable or shoelace marked with a finger and laid against a ruler is accurate to about a quarter inch.
An unpadded bra, or none
Measure the band bare and the bust in a thin unlined bra or bare skin. Padding, moulding and push-up all add inches that are not yours and inflate the cup by half a size or more.
A mirror
The tape has to be level all the way round, including across your back. You cannot check that by feel, and a tape that rides up at the back reads the band too tight.
Two minutes
Stand upright, arms relaxed, normal posture. Do not hold your breath or pull your shoulders back. Morning, mid-cycle, before exercise gives the most repeatable reading.
How to measure your bra size
Two numbers do all the work. The first sets your band, the second sets your cup, and the third step is a subtraction. Record both in inches to the nearest half inch, or switch the calculator to centimetres. Most people are wearing a band too loose and a cup too small, so measure fresh rather than trusting the label in your drawer.
Measure directly under your bust
Wrap the tape around your ribcage immediately beneath the breast tissue, where an underwire would sit. Pull it snug — firm enough that you cannot slide more than a finger underneath, because a bra band is elastic and will always be tighter than a tape.
Exhale fully, then read the number. Round to the nearest half inch. This is your band measurement; the calculator rounds it to the nearest even inch for you.
Measure across the fullest part
Keep the tape level front to back and let it rest on the fullest point, usually the nipple line. Do not pull it tight. Compressing the tissue here shrinks your cup, and is why so many people end up in a D when they are an F.
If your breasts are soft or fuller at the bottom, lean forward about 45 degrees so tissue falls naturally, then measure.
Subtract the band from the bust
Every whole inch of difference is one cup letter: 1″ is A, 2″ is B, 3″ is C, 4″ is D, 5″ is DD, 6″ is DDD in US lettering and E in UK, 7″ is a US G and a UK F. Put the rounded band number in front of the letter and that is your size. A 33″ underbust rounds to a 34 band; with a 38″ bust the difference is 4″, so a 34D. The calculator above does this arithmetic and adds your sister sizes and stock.
What the number and the letter actually mean
A bra size is two independent measurements wearing one label. Treating them as one thing is why sister sizes confuse people.
The band is the number
Your band measurement rounded to the nearest even inch. That is the whole calculation. We use the modern method, which means no plus-four: adding four inches was a workaround for the non-stretch fabrics of the 1950s and has been wrong for decades.
The band does around eighty percent of the support work. If it rides up your back it is too loose, not too tight. Most problems that look like a strap issue trace back to a band a size too big.
The cup is the difference
Subtract the band from the bust. Each whole inch of difference is one cup step, starting at AA for zero. A five inch difference is a US DD. A seven inch difference is a US G and a UK F, which is where the two systems visibly part company.
A cup letter is not an absolute volume. A 30D and a 38D hold very different amounts. The letter only means something attached to its band number.
| Difference | US cup | UK cup | EU cup | AU cup |
|---|
The row matching your measurements is marked. US and UK agree up to a five inch difference and diverge from six inches onward — the single biggest source of confusion between American and British brands.
Bra size chart
Every band and cup combination we stock, with live product counts. Pick a cell to see the measurements that produce it and jump to that size. Greyed cells are combinations we do not currently carry.
Sister sizes, and when to use one
Sister sizes are different labels holding the same cup volume. Go down one band and up one cup, or up one band and down one cup, and the cup itself stays the same. This is what to reach for when your size is sold out, or when the cup is right but the band is not.
Volume is constant across the row. What changes is how tight the band sits on your ribcage, and therefore how much of the support comes from the band rather than the straps.
The band rides up at the back
The band is too loose. Go down one band and up one cup. A 36C becomes a 34D. The cup is unchanged, the band finally does its job, and the straps stop digging.
The band digs in or you cannot breathe
The band is too tight. Go up one band and down one cup. A 34D becomes a 36C. Try this before assuming you need a wider back or a longer hook row.
Bra size conversion
We carry US, UK and European brands side by side, so the number on the label depends on where the bra was cut. Panache and Freya print UK. Wacoal and Le Mystère print US. Chantelle prints French. These two tables reconcile them.
Band size conversion
| US | UK | EU / IT | FR / ES | AU / NZ | JP |
|---|
US and UK band numbers are identical. European bands are metric underbust bands, French runs fifteen higher than European, and Australian sizing uses a dress-size run.
Cup letter conversion
| Difference | US | UK | EU | AU |
|---|
Australia follows the UK cup ladder. France follows the European one. The doubled letters — FF, GG, HH — exist only in UK and Australian sizing, which is why a Panache label looks unfamiliar to a shopper used to American brands.
How to measure band, bust and cup size
The two steps above are enough for most people. This is the longer version: what each measurement is for, where it goes wrong, and how to take it when you have no tape, no bra, or a bust that measures differently standing and leaning.
How to measure bra band size
Your band is the circumference of your ribcage in the crease directly under the breast, the inframammary fold, where the wire of an underwired bra sits. Measure it bare or in a thin unlined bra, never over padding, and never over a bra whose band you are testing. Wrap the tape level all the way round, check the back in a mirror, pull it snug enough that only a finger slides underneath, exhale fully and read. Round to the nearest even number: bras are only cut in even bands. A 31″ reading is a 32, a 33″ is a 34. When in doubt round down, because bands stretch with wear and a firm band lasts longer; if the smaller band digs in or restricts breathing, sister up.
Do not add four, or two, or five inches. Every plus-something rule dates from rigid pre-1960s elastic and hands you a band that rides up the back and pushes the load onto the straps. The comparison table below shows how far off it lands.
How to measure bust size
Your bust measurement is the circumference around the fullest part of the chest, usually across the nipple line but not always; find the point where the tape reads largest. Wear a thin unlined bra that fits or go without if you can hold the tape steady. Keep it level front to back, snug enough not to slip, loose enough not to flatten anything. Compressing tissue is the classic way to lose a whole cup size here.
If you are a C cup or above, or your tissue is soft or fuller at the bottom, take a second reading leaning forward to about 45 degrees so the breast falls away from the chest wall. If the leaning number is more than half an inch larger, use it. A bra that fits the fuller reading fits all day; one fitted to the smaller reading spills by mid-afternoon.
How to measure cup size
A cup size is not measured directly. It is the difference between the two numbers you already have: bust minus band, in whole inches. One inch is A, two is B, three is C, four is D, five is DD. At six inches the systems split: DDD in US lettering, E in UK, F in Europe. Seven inches is a US G and a UK F. The size chart above shows every step, and the letter only means something attached to its band number: a 32D and a 36D are different volumes; a 32D and a 34C are the same.
Round the difference to the nearest whole inch. If you land on a half, try the larger cup first; a cup slightly too big can be closed with the straps, one slightly too small cannot be made to hold what it will not hold.
How to measure without a tape measure
Wrap a non-stretch string, ribbon, phone cable or shoelace exactly as you would the tape, pinch or mark where it overlaps, then lay it flat along a ruler, a yardstick or the edge of a sheet of A4 or letter paper (11.7″ and 11″ long respectively). Keep the string flat and level and you will be within a quarter inch, which is closer than the rounding rules need.
How to measure without a bra
The band is better measured without one. For the bust, going braless works if your tissue holds its position; if it settles low or the tape slips, either wear a thin unlined bra or take the leaning-forward reading, which lets the tape sit on the fullest point without help from a cup. Never measure over a padded, moulded or push-up bra: it will read a cup or more too large.
Measuring in centimetres
Switch the calculator to centimetres and enter the readings as they are. Or convert by hand: divide the underbust by 2.54 and round to the nearest even inch for the band; for the cup, every 2.5 cm of difference between bust and underbust is one letter, so 7.5 cm is a C and 12.5 cm is a DD. An 84 cm underbust with a 94 cm bust is a 34D, which European brands label 75D. The conversion page has the full centimetre table.
Why the plus-four method gives you the wrong size
If a department store once measured you into a 36B when you suspected a 32D, you were fitted with the plus-four method: add four inches to the underbust to get the band. It was written for the non-stretch bands of the 1950s and has never been updated. It is the single biggest cause of the too-loose band that most people are wearing today.
| Underbust | Plus-four band | Direct band | Result |
|---|---|---|---|
| 28″ | 32 | 28 | Two bands too loose. The 28 band barely exists in that fitting. |
| 30″ | 34 | 30 | Two bands too loose, and the cup letter drops two to compensate. |
| 31″ | 36 | 32 | Rounded up twice. A 32D wearer is handed a 36B. |
| 32″ | 36 | 32 | Two bands too loose. |
| 34″ | 38 | 34 | Two bands too loose. |
| 36″ | 40 | 36 | Two bands too loose. |
| 38″ | 42 | 38 | Two bands too loose. |
To keep the cup volume roughly right on the oversized band, plus-four fitters also dropped the cup letter, which is how a 32D becomes a 36B. Both numbers are wrong. The 32D fits, and the 36B rides up, stretches out within weeks and moves the whole load onto the straps. A chronically loose band is a structural problem as well as a comfort one; above a D cup the unsupported weight is real.
Six measuring mistakes, and how to tell if your current bra fits
If the calculator hands you a size that feels wildly off from what you wear, one of these is usually why. Then use the table to read what your current bra is telling you.
What your current bra is telling you
| Symptom | What it usually means | What to try next |
|---|---|---|
| Band rides up the back | Band too loose; the most common fault. | Sister down: 36C to 34D. |
| Cup gapes at the top | Cup too big, or a loose band pulling the cup off the chest. | Smaller cup on the same band; sister down if the band is loose too. |
| Spills over the top of the cup | Cup too small. | Larger cup on the same band; sister up if the band is also tight. |
| Wire pokes at the side | Cup too small for the breast root, pushing the wire out. | Larger cup, same band. |
| Centre gore floats off the chest | Cup too small, or wires too narrow for your chest. | Larger cup first; if it still floats, a different cut. |
| Wire sits on breast tissue | Wires too narrow for the root. | A brand with wider-set wires. |
| Straps dig into shoulders | Band too loose; the straps are carrying what the band should. | Tighten a hook, or sister down. |
| Band right, bra still feels wrong | Brand pattern does not match your shape. | A different cut: full cup, balconette, plunge. See shape. |
When to re-measure your bra size
Every six to twelve months as a baseline, and whenever any of these happens. Cup volume in particular moves more than people expect; the monthly cycle alone can shift a bust measurement by half a cup.
Weight change of ten pounds or more
In either direction. The cup often changes before the scale shows much, and the band follows.
Your cycle
The week before a period adds fluid and volume, often half an inch to an inch of bust. Measure mid-cycle for a base size, or measure twice and fit to the smaller reading for everyday bras.
Hormonal contraception or HRT
Measure three months after starting or switching. Hormone therapy of any kind can move the cup by a letter or more; during the first years of HRT re-measure every three to six months.
Pregnancy and postpartum
Measure each trimester and expect the cup to rise at least a size when milk comes in. While nursing, fit to the fuller state and expect the size to move for months.
Menopause
Tissue softens and often settles lower, so the standing measurement under-reads. Use the leaning reading and expect to move toward unlined or stretch-cup styles.
Training, surgery, or a bra that suddenly feels wrong
Adding or dropping weight training, any chest, shoulder or abdominal surgery, or a familiar bra that stops fitting: your body has changed even if you cannot see it.
Sports, strapless, nursing and everyone else
The measurement is the same; the allowance changes. Sports bras want the band firm because impact support is band-led; compression styles often run small, encapsulation styles closer to true size. Strapless bras usually need a band one size down, since there are no straps to help. Nursing bras are fitted to the fuller state with a stretch cup. Bra size is chest geometry, not gender: anyone with breast tissue uses the same band-and-bust arithmetic. This is fit advice, not medical guidance.
Size gets you close, shape gets you fitted
Two people can be a true 34F and need completely different bras. Volume distribution, root width and how full you are at the top decide which cut works. Find the description that sounds like you.
Full on top
Most of your volume sits above the nipple line. Plunges and demis tend to spill, and moulded cups cut in across the top.
Full on bottom
Volume sits below the nipple line and the upper cup stays soft. Rigid moulded cups gape at the top even in the right size.
Wide set
A gap between the breasts and volume sitting toward the underarm. Plunges leave the cups half empty at the centre.
Close set
Little space between the breasts. A tall centre gore presses uncomfortably and will not lie flat no matter what size you try.
Soft or relaxed tissue
Tissue moves and settles through the day, so a single measurement undersells you. Measure leaning forward and fit to the fuller reading.
Eight fit problems and what they are telling you
A calculator gives you a starting size. Your body gives you the correction. Match the symptom, apply the adjustment, and re-run the numbers if you need to.
Browse bras by size
Every band and cup we stock, from 28D through 48F, with live counts. Coverage is uneven by design: a 28 band runs to J while a 46 band stops at F, because that is what the brands cut.
Bra sizing and measuring, answered
How do I measure my bra size at home?
How accurate is this bra size calculator?
How do I measure my band size?
How do I measure my bust size?
How do I measure my cup size?
Can I measure without a tape measure?
Should I measure over a bra or without one?
Is the plus-four method accurate?
My band measurement is an odd number. What do I do?
What is my bra size if I am between two sizes?
Why is my measured size different from what I usually wear?
What if my bust measures smaller than my band?
Is DDD the same as F?
Which is bigger, DD or F?
How often should I re-measure?
Does my bra size change during my period?
Does this work for nursing, sports and strapless bras?
What is the average bra size?
Why does my size fit differently between brands?
What if my size is sold out?
How this calculator works
No proprietary algorithm and nothing hidden. Two subtractions and a lookup, published here so you can check it against a bra you already own and trust.
Band, then cup
The band comes straight from the underbust measurement, rounded to the nearest even inch and clamped to the 28 to 48 range that bras are actually made in. The cup is the whole-inch difference between bust and band, read off the ladder for whichever system you are shopping.
Every other number on this page — the sister sizes, the conversions, the grid — is derived from those two values. Nothing is stored on a server and nothing is sent anywhere. Your measurements stay in your own browser.
What we deliberately do not do
No plus-four. Adding four inches to the underbust was a fabric workaround from an era of rigid, non-elastic bands. Applied to a modern band it produces a size that rides up and pushes the support onto the straps.
No single house chart. We carry US, UK and European brands, and forcing them into one table would be wrong for two thirds of the catalogue. The result shows five systems because the label you are buying only prints one.
No invented brand charts. Where a brand cuts differently from the standard, we say so rather than quietly adjusting the number.
No stored measurements. Nothing leaves your browser, nothing is attached to your account, nothing is used for marketing.
Ranges we cover
Bands 28 to 48. Cups A to K in UK lettering, A to DDD and beyond in US. Not every combination exists in every band, and the size directory shows the real coverage rather than an idealised grid.
Shop it, in stock, today
555 bras from 28D through 48F, and free US shipping over $50.
Fitting method reviewed against UK and US brand specifications. Measurements never leave your browser.