Bra Size 40: The 40 Band
A 40 band fits a snug underbust of 39 to 40 inches (99 to 102 cm). Every cup letter on it describes the same ribcage with more or less bust over it, from 40A to 40K. Here is the whole band: its measurements, every cup with its sisters and conversions, who stocks it, and how it should fit.
The 40 is the snug underbust 39 to 40 inches, nothing added: EU 90, FR 105, AU 18. The cup letter is the bust over that band, one inch per letter. A 40 that rides up is a band too big, fixed by a 38 with one cup up; one that digs is a band too small.
What a 40 band means
The band number is a ribcage measurement. Wrap a tape snugly around the torso directly under the breasts, level all the way round, on a normal exhale, and read it: 39 or 40 inches is a 40 band. Nothing is added. Charts that add four or five inches would call the same ribcage a 44, which is why so many people have worn a 44 band that rides up and a cup two letters too small; the methodology page explains why this site never adds inches.
A snug tape reading of 39 rounds up to the 40; a reading of 41 rounds up to the 42. When the tape lands on the odd number it is worth trying both neighboring bands with the cup adjusted a letter, which is what sister sizes are for. Bands are cut in two-inch steps because the elastic covers the inch between; a 40 on the loosest hook fits 39 and 40, and the tighter hooks are there for when the elastic relaxes.
Every cup on the 40 band
Same ribcage in every row; only the bust changes. Each letter is one more inch of bust over the 40-inch band, so a 40C is a 43-inch bust and a 40DD a 45-inch one. The two sisters are the same cup on the bands either side, and the UK and EU labels are the same rung in the other alphabets. Tap a size for its full guide.
| Size | Bust | Over band | Sister sizes | UK · EU |
|---|---|---|---|---|
| 40A | 41″ · 104 cm | +1″ | 38B · 42AA | 40A · 90A |
| 40B | 42″ · 107 cm | +2″ | 38C · 42A | 40B · 90B |
| 40C | 43″ · 109 cm | +3″ | 38D · 42B | 40C · 90C |
| 40D | 44″ · 112 cm | +4″ | 38DD · 42C | 40D · 90D |
| 40DD | 45″ · 114 cm | +5″ | 38DDD · 42D | 40DD · 90E |
| 40DDD | 46″ · 117 cm | +6″ | 38G · 42DD | 40E · 90F |
| 40G | 47″ · 119 cm | +7″ | 38H · 42DDD | 40F · 90G |
| 40H | 48″ · 122 cm | +8″ | 38I · 42G | 40FF · 90H |
| 40I | 49″ · 124 cm | +9″ | 38J · 42H | 40G · 90I |
| 40J | 50″ · 127 cm | +10″ | 38K · 42I | 40GG · 90J |
| 40K | 51″ · 130 cm | +11″ | — · 42J | 40H · 90K |
Cup letters agree across systems up to D; above it the US runs DD, DDD, G, H, the UK DD, E, F, FF and the EU E, F, G, H. The cup size chart lays the three alphabets side by side.
Sister sizes on and off the 40 band
A sister size holds the same cup volume on a different band: one band down and one cup up, or one band up and one cup down. The table shows two steps in each direction from every 40 size, which is as far as sister sizing is useful; beyond that the band is four inches from your ribcage and no cup letter fixes it. Use the first step when a brand runs tight or loose, or when the cups fit and the band does not. Use the second only to understand why a 44 with a small cup never fitted.
| 40 size | Band down | Two down | Band up | Two up |
|---|---|---|---|---|
| 40A | 38B | 36C | 42AA | — |
| 40B | 38C | 36D | 42A | 44AA |
| 40C | 38D | 36DD | 42B | 44A |
| 40D | 38DD | 36DDD | 42C | 44B |
| 40DD | 38DDD | 36G | 42D | 44C |
| 40DDD | 38G | 36H | 42DD | 44D |
| 40G | 38H | 36I | 42DDD | 44DD |
| 40H | 38I | 36J | 42G | 44DDD |
The sister size calculator explains which direction to step from any symptom; the bra too big and bra too small pages read the signs.
The 40 band in every sizing system
The band converts by formula: EU is 2.5 times the US number minus 10, French and Spanish sizes are the EU number plus 15, Australian and New Zealand sizes are the US number minus 22, and Italian sizes are half the US band minus 14. The cup letter does not convert by matching: a 40DD is a 40DD in the UK but an 90E in Europe. The equivalent chart lists every 40 size in all six systems and the converter does any pair.
Who stocks the 40 band
The 40 band is the first band mass-market ranges cut with fewer cups. Mass-market lines still cut it, usually to a DDD, and full-figure and full-bust specialists cut it to a K, so the size you can find depends on the cup more than the band. A 40B or 40C is easy; a 40G is a specialist purchase. Two things change at this band. Wires get wider, because cups at the same letter are broader on a larger ribcage, and bands get taller, because a wider wing distributes load better on a softer torso. A 40 band that rides up is loose; a 40 band that folds is usually too short in the wing rather than too small.
Brands whose charts cut the 40: Elomi, Cacique, Parfait, Wacoal, Le Mystere, Playtex and Bali carry it fully. Each brand page on this site lists the exact band and cup range and notes how that brand’s 40 runs; the best bras by size hub groups them by the cup you need.
How a 40 band should fit
- Fasten on the loosest hook. A new 40 should hold there, level around the ribcage, with the tighter hooks in reserve for when the elastic relaxes.
- Two fingers, flat, and no more. If a fist fits under the band, the 40 is too big for your ribcage and the 38 is the one to try; if two fingers will not slide under it, the 42 is.
- Raise your arms. The band stays put. If it lifts at the back or gaps away, it is too big regardless of how the cups look.
- Check the marks. A snug 40 leaves faint lines that fade within minutes. Deep grooves an hour later mean the band is too small; no marks at all usually mean it is doing nothing.
- Then read the cups. With the band right, any gap or overflow is the cup letter, and the table above shows the next size in either direction.
The fit guide walks all six checks with diagrams; the band riding up and band digging in pages cover the two band symptoms in detail.
The 40 band: answered
What underbust is a 40 band?
A snug underbust of 39 to 40 inches (99 to 102 cm), measured firm around the ribcage directly under the breasts with nothing added. A 39 reading rounds up to the 40 band; a 41 rounds up to the 42.
Is a 40 band big or small?
On the larger side of the range. The 40 is the first band mass-market ranges cut with fewer cups; full-figure specialists treat it as a core size.
What is a 40 band in European sizes?
EU 90, French and Spanish 105, Australian 18, Italian 6. The band is the same 39 to 40 inch ribcage in every system; only the label changes. Cup letters convert by position, not by matching, so check the size page for the full label.
Can I wear a 38 or a 42 band instead of a 40?
Only as a sister size, with the cup adjusted to keep the volume: a 40D is a 38DD or a 42C. A band two inches off your measurement on the loosest hook will either ride up or dig, so the sister move is for brands that run tight or loose, not a substitute for measuring.
Which cups come on a 40 band?
On this site, 40A to 40K in US letters. In stores, elomi, cacique, parfait, wacoal, le mystere, playtex and bali carry it fully. The cup range narrows at both ends of the band ladder: small bands are cut deep by specialists and shallow by nobody, large bands are cut in the middle cups and rarely at the extremes.
Opens HauteFlair’s own hub page; choose the 40 band there. HauteFlair is owned by the same company as Brasize.ai; that relationship never changes the sizing math, charts, or fit advice on this page. How this site makes money.
Confirm the band, then the cup
Two measurements, no inches added, sister sizes attached.
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