How should a bra fit? Check yours in a minute
Put on the bra you wear most, tell us its size, and tick what you notice. We'll work out whether the band, the cups or both are off, and give you the exact size to try next.
Your next size appears here on a fitting card, drawn beside the size you wear now.
- Band level all the way round and snug on the loosest hook
- Cups smooth: no spilling over, no gaps or wrinkles
- Centre flat against the breastbone
- Wires around the breast, not on it
- Straps stay put without digging in
What brand fit guides say
Four brands' own fit advice, quoted from their pages on 26 September 2026. They agree on the direction every time; the fit check follows that direction and works out the size.
| Problem | Marks & Spencer | Victoria's Secret (UK) | ThirdLove | SKIMS | Our move |
|---|---|---|---|---|---|
| Band rides up | You might need a smaller band size. | Try a tighter hook or go down a band size. | The band should be parallel to the floor and should not ride up. | – | Band down |
| Straps dig in | If they are doing all the work, your band may be too big. | They should never dig into your shoulder. | If your straps dig in, your band may be too loose. | Adjust shoulder straps so they are comfortably snug. | Band down |
| Band digs in | – | Try a looser hook. Still tight? Try a larger band and smaller cup size. | – | – | Band up |
| Spilling over | Spilling out? Try a bigger cup. | If you are spilling over, go up a cup size. | A cup that is too small (overflowing). | Spillage on the top or the sides: they may be too small. | Cup up |
| Centre lifts off | If it is lifting away, you need a bigger cup size. | – | If the center gore stands away from your body, your cups are too small. | A gap indicates the cup is too small. | Cup up |
| Wires poke | Wires should not poke, rub or press on breast tissue; a different size or style could help. | – | The underwire should not lay on your breast tissue. | – | Cup up, or another style |
| Cups gape | Gaping or creasing? A smaller cup might fit better. | Cups gaping? Go down a size. | A cup that is too big (puckering). | – | Cup down |
Our read: no guide disagrees with another on which way to move. Only Victoria's Secret and ThirdLove pair a band change with the opposite cup change, and none works out the size that results. That step is the sister-size rule: one band down is worth one cup letter up, so a band fix keeps the same cups only if the letter changes too.
Three problems people search for by name
Each one is a single symptom in the checker above. Tick it there and we work out the size; here is the short version.
Bra band too loose
"bra band too loose" gets 1,000 US searches a month. A loose band rides up at the back and lets the straps take the weight that the band should carry. Fix: one band down, and the cup letter goes up one to keep the same cup volume, for example 34D to 32DD.
Check my size for a loose band
Bra straps falling down
"bra straps falling down" and "bra straps keep falling down" together get about 600 US searches a month. Straps that slide off the shoulder are usually a band problem, not a strap problem: the band is too loose to hold the bra in place, so the straps do the work and then give up. Fix: the same one band down as above.
Check my size for slipping straps
Bra cups too big or gaping
"bra cups too big" and "bra cups gaping" get about 280 US searches a month between them. Gaps or wrinkles in the cup mean it is too big for you. Fix: one cup letter down on the same band, for example 34D to 34C.
How the fit check decides
The same engine as the calculator and the sister-size chart, so every answer lands on a real label in six systems.
Band first
The band does most of the lifting (ThirdLove puts the straps at about 10% of the work). A band that rides up or leaves the straps doing the work is too loose: we move one band down. Going down a band shrinks the cups too, so we move the cup letter up one to keep the same volume. That is a sister size: 34D becomes 32DD.
Then the cups
Spilling, a centre that lifts off and wires sitting on breast tissue all mean the cups are too small: one letter up on the same band. Gaping or wrinkles mean one letter down. Both moves together are common: a 34D that rides up and spills becomes 32DD for the band, then 32E for the cups (US 32DDD).
When the signs disagree
If you tick a band that is both too loose and too tight, or cups that both spill and gape, we don't guess. Mixed band signs usually mean the band sits at an angle or has stretched; mixed cup signs usually mean the cup shape, not the size, is wrong for you. The result says so and keeps your size.
Before you buy a new size
- Try the bra on its loosest hook, level at the back. A band that only fits on the tightest hook has stretched (Victoria's Secret suggests a tighter hook before a smaller band).
- Lean forward and settle the breast tissue into each cup, then stand up and check again.
- Loosen the straps: if the bra stays put without them, the band is doing its job.
A fit check can't see your shape. If two sizes in a row still fail, a fitter can tell you what we can't. For the size you should start from, use the calculator.
Quick answers
How should a bra fit?
The band sits level and snug on the loosest hook and does most of the lifting. The cups hold all the breast tissue with no spilling or gaping, the centre between the cups lies flat on the breastbone, the wires sit around the breast rather than on it, and the straps stay put without digging in.
Why does my bra ride up at the back?
The band is too loose. Try the tightest hook first; if it still rides up, go down one band and up one cup letter to keep the same cup volume, for example 34D to 32DD.
Why do my bra straps dig in?
Usually because the band is too loose and the straps are carrying the weight. Loosen the straps; if the band then rides up, go down a band and up a cup.
What does it mean if the centre of my bra does not touch my chest?
The cups are too small to let the centre sit flat, so go up one cup letter on the same band. Less often, the wires are too narrow for you.
Next steps
- Bra size calculatorTwo methods side by side, and why they disagree
- How to measureBand, bust and the leaning check, step by step
- Sister sizesThe whole chart, and what to try when the band rides up
- UK to US converterAny size in any of six systems
- International size chartUK, US, EU, FR, AU and Japan on one grid
- Cup sizes guideWhat a cup letter means, and why it changes by band
- Brand size chartsVictoria's Secret, ThirdLove, Wacoal, SKIMS, M&S and Freya, read side by side
- 30DSister sizes, conversions and fit notes
- 32DDSister sizes, conversions and fit notes
Sources
Each source was opened and checked on the date shown, or on 25 September 2026. Where sources disagree, the page says so instead of picking one silently.
- Marks & Spencer, "How to Measure Bra Size": fit checks; sister sizing; a tape gives a rough starting point (opened 26 September 2026)
- Victoria's Secret UK, "Measure Your Bra Size": band = snug underbust rounded to the nearest even number; fit fixes; sister table (opened 26 September 2026)
- ThirdLove, "Bra Size Calculator & Chart": bands 32 to 44, cups AA to H with half cups; calculator run with 6 measurement pairs (opened 26 September 2026)
- SKIMS, "Bra Size Guide": underband and overbust chart, sizes 30AA to 46H, US/UK/EU/AU cup table (opened 26 September 2026)
- White J, Scurr J. Evaluation of professional bra fitting criteria for bra selection and fitting in the UK. Ergonomics 2012;55(6):704-711: 45 women; the traditional method overestimated band and underestimated cup
- McGhee DE, Steele JR. Optimising breast support in female patients through correct bra fit. J Sci Med Sport 2010;13(6):568-572: 104 women in Australia; 85% in ill-fitting bras