An estimated 8 out of 10 women wear the wrong bra size. The result? Straps that dig, bands that ride up, cups that gape or spill, and underwires that sit in all the wrong places. This guide walks you through the exact measurements you need, an interactive calculator that does the math for you, and a complete breakdown of how to read your results, including sister sizes and international conversions.
1. What You'll Need
The flexible kind used for sewing or tailoring. A rigid metal tape will not give an accurate read.
A push-up, padded, or sports bra will distort your bust measurement. A t-shirt bra without padding works well, or measure topless.
To make sure the tape is straight and level, especially around the back.
Honestly, that's it. The math takes seconds. The hardest part is keeping the tape level.
2. How to Measure
Two measurements determine your bra size: your band (the ribcage just under your bust) and your bust (the fullest part of your chest). Take both standing up straight, with your arms relaxed at your sides.
Measure Your Band (Underbust)
Wrap the tape snugly around your ribcage directly under your bust, where the band of a bra would sit. The tape should be parallel to the floor and level all the way around — check the back in the mirror.
Pull the tape firm but not tight. Exhale fully, then take the reading at the end of the exhale.
Record this number: Underbust = ____ inches (or ____ cm)
Measure Your Bust (Fullest Part)
Wrap the tape around the fullest part of your bust, usually right across the nipples. Keep the tape level — it should be parallel to your band measurement, not slanted up or down.
Hold the tape gently against your skin. Don't pull it tight enough to compress, or the cup will measure too small.
Record this number: Bust = ____ inches (or ____ cm)
Plug Both Numbers Into the Calculator Below
That's it. The calculator does the rest — band sizing, cup letter, sister sizes, and international conversions all in one go.
3. The Bra Size Calculator
Enter both measurements below. The calculator will instantly return your US size, UK size, EU size, and sister sizes worth trying.
Measure snugly under your bust, on the exhale.
Measure across the fullest point of your bust.
Your recommended size
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US Size
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UK Size
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EU Size
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FR / ES Size
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Sister sizes to also try
If your calculated size feels too tight or too loose in the band but the cup is right (or vice versa), these sizes hold the same cup volume with a different band.
Now that you know your size, browse styles cut for your fit.
Shop HauteFlair Bras4. Understanding Your Result
A bra size has two parts: a band number and a cup letter. Here's exactly what the calculator did with your measurements.
The band number
Your band number comes from your underbust measurement, rounded to the nearest even number in inches. For example, an underbust of 31 inches rounds to a 32 band. An underbust of 34.5 inches rounds to a 34 band. The band carries roughly 80% of the bra's support, so getting this number right matters more than getting the cup right.
The cup letter
Your cup letter comes from the difference between your bust and your band, in inches. Each inch of difference equals one cup size up.
| Bust − Band (inches) | US Cup | UK Cup |
|---|---|---|
| Less than 1" | AA | AA |
| 1" | A | A |
| 2" | B | B |
| 3" | C | C |
| 4" | D | D |
| 5" | DD | DD |
| 6" | DDD / F | E |
| 7" | G | F |
| 8" | H | FF |
| 9" | I | G |
| 10" | J | GG |
| 11" | K | H |
Note: US and UK cup labels diverge starting at the 6-inch difference. A US 32DDD is roughly equivalent to a UK 32E. This is why the calculator returns both.
Cup size quick answers
- Is DDD the same as F?
- In US sizing, DDD is equivalent to an F cup. In UK sizing, DDD is equivalent to an E cup. Same volume, different label.
- Is a DD bigger than a D?
- Yes. DD is one cup size larger than D — a 5-inch bust-to-band difference instead of 4 inches.
- Is a DD bigger than an F?
- No. The cup sequence goes A, B, C, D, DD, DDD/F, G — so an F cup is two sizes larger than a DD.
- Is cup size B bigger than C?
- No. C is one full cup size larger than B. The letters get larger as cup volume increases.
- Are D cups big?
- Cup size is always relative to band size. A 30D and a 38D hold very different volumes — the 38D is significantly larger. By itself, "D" doesn't mean big or small without the band number.
- Is the number the band or the cup?
- The number is the band size (your underbust circumference). The letter is the cup size (the bust-to-band difference). So in 34C, 34 is the band and C is the cup.
5. Sister Sizes Explained
Two different bra sizes can hold the same volume of breast tissue. These are called sister sizes, and they're the single most useful concept in bra fitting.
The rule: as the band number goes up, the cup letter goes down by one to keep the cup volume the same. As the band goes down, the cup goes up.
Example sister-size family for a 34C
30
DD
32
D
34
C
36
B
38
A
When to size up the band, down the cup: the cups fit but the band feels tight, rides up in the back, or leaves marks.
When to size down the band, up the cup: the band rides loosely or you can pull it more than two inches off your back, but the cup is full or spilling.
6. International Size Conversion
Many of the brands HauteFlair carries are designed in Europe and use UK, French, Italian, or Australian sizing. Use this chart to translate.
| US Band | UK Band | EU / Italian | FR / ES | AU / NZ | JP |
|---|---|---|---|---|---|
| 30 | 30 | 65 | 80 | 8 | 65 |
| 32 | 32 | 70 | 85 | 10 | 70 |
| 34 | 34 | 75 | 90 | 12 | 75 |
| 36 | 36 | 80 | 95 | 14 | 80 |
| 38 | 38 | 85 | 100 | 16 | 85 |
| 40 | 40 | 90 | 105 | 18 | 90 |
| 42 | 42 | 95 | 110 | 20 | 95 |
| 44 | 44 | 100 | 115 | 22 | 100 |
Cup Letter Conversion
| US Cup | UK Cup | EU Cup | AU Cup |
|---|---|---|---|
| A | A | A | A |
| B | B | B | B |
| C | C | C | C |
| D | D | D | D |
| DD | DD | E | DD |
| DDD / F | E | F | E |
| G | F | G | F |
| H | FF | H | FF |
| I | G | I | G |
| J | GG | J | GG |
7. Common Fit Issues & Fixes
Once you have your size, here's how to read the bra on your body and adjust if something isn't sitting right.
Band rides up the back
Cause: Band is too loose.
Fix: Go down one band size and up one cup. (38C → 36D)
Band digs in or feels suffocating
Cause: Band is too tight.
Fix: Go up one band size and down one cup. (32D → 34C)
Cups gape or pucker at the top
Cause: Cups are too big, or the style is wrong for your shape.
Fix: Go down one cup. If you have shallow or wider-set breasts, look for a plunge or balconette cut.
Cups overflow (the "double bust" effect)
Cause: Cups are too small.
Fix: Go up one or two cup sizes, keeping the band the same.
Underwire sits on breast tissue
Cause: Cups are too small — the wire should encircle the breast, not press into it.
Fix: Go up a cup. If the wire still doesn't sit flat against your sternum, try a different brand — wire shapes vary.
Straps dig into shoulders
Cause: The band isn't doing its job, so the straps are carrying all the weight.
Fix: Tighten the band or go down a band size. Straps should hold the cups in place, not lift the bust.
Center gore floats away from chest
Cause: Cups are too small, so they push the wire forward.
Fix: Go up a cup size. The center gore should sit flat against your sternum.
8. Frequently Asked Questions
How accurate is this bra size calculator?
The calculator gives you a strong starting point — typically within one band size and one cup size of your true fit. The math is precise, but bras are made by humans for human bodies, and shape, fabric, breast tissue density, and brand cut all introduce variation that pure measurements can't predict. Treat the result as your "first-bra-to-try" size, then use the fit checks above (band level, cups smooth, gore flat against sternum, straps not bearing weight) to confirm.
Can I use this if I'm pregnant or breastfeeding?
You can, but expect your size to fluctuate significantly throughout pregnancy and the postpartum period — sometimes by two band sizes and three or more cup sizes. Re-measure every 4 to 6 weeks during pregnancy and weekly while nursing in the early months. For breastfeeding specifically, look for soft nursing bras with stretch fabric that accommodates the daily volume changes between feedings, and skip underwire until your milk supply has fully regulated to avoid clogged ducts.
How often should I re-measure?
Every 6 to 12 months, and any time you experience a change of more than a few pounds in either direction, a pregnancy, breastfeeding, hormonal shift, or major fitness change. Most women will wear three to four different sizes across their lives.
My measurements give me a half-size band. What do I do?
Bra bands only come in even numbers (US sizing). If your underbust measures 33 inches, try a 34 first. If the band feels loose, go down to a 32 and up one cup to keep the volume.
The calculator gave me a size I've never worn before. Is it wrong?
Probably not. Most women wear the wrong size — typically a band that's too big and a cup that's too small. If your new size feels strange, that's expected. Try it on, walk around, and trust the fit checks above (band level around the body, cups smooth, gore flat, straps not bearing weight).
Do brands fit differently even at the same size?
Yes — significantly. Wire shape, cup depth, strap placement, and fabric stretch all vary. A 34D in one brand can fit completely differently from a 34D in another. Use the size chart on each product page on HauteFlair, and don't hesitate to use sister sizes as a starting point when trying a new brand.
What about for nursing, sports, or strapless bras?
Start from your calculated size, then adjust by category. Nursing bras typically run truer to size but need to accommodate cup-size fluctuation throughout the day — a stretchy fabric helps. Sports bras often run small in the band for compression. Strapless bras almost always need to go down one band size for extra grip, and up one cup to compensate.
Can I measure over a bra?
For the underbust (band) measurement, yes — as long as the bra band itself isn't padded. For the bust measurement, only over an unpadded, lightly lined bra. A push-up or padded bra adds at least one cup size to the reading.
What if I'm between sizes?
Try both. Keep what fits. If you're between band sizes, go to the smaller band — bands stretch with wear. If you're between cup sizes, go to the larger cup; an empty cup is easier to live with than a spilling one.
I have asymmetrical breasts — which side do I measure?
Measure the larger side and fit to that. You can use a removable cup insert on the smaller side, or choose styles with stretch lace cups that adapt to both sides naturally.
Now that you know your size, find your fit.
HauteFlair carries over 50 designer brands across band sizes 28 through 46 and cups AA through K. Filter by your size on every collection page.
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