US 40DDD converts to UK 40E, EU 90F, French 105F, and Australian 18E.
For the full breakdown, see our best 40DDD Bras guide.
Shopping for bras gets confusing the moment you cross a border or open a foreign brand’s size chart. The US 40DDD bra size equivalent isn’t one number — it shifts with each country’s sizing system, and even then, brands don’t always agree. If you wear a 40DDD, the strap measurement stays roughly the same everywhere (about 39–41 inches around the ribcage), but the cup letter changes depending on where the label was printed.
Here’s the clean conversion table you need, plus the sister sizes that make fitting easier and the mistakes that send shoppers home with the wrong bra.
The Quick Conversion Chart For 40DDD
Most international charts agree on these equivalents for a US 40DDD, though you’ll see minor variations between brands.
| Sizing System | Equivalent Size | Notes |
|---|---|---|
| US / Canada | 40DDD | Also written 40E by some US brands |
| UK | 40E | Most common conversion; UK skips DDD |
| EU | 90F | Band measured in centimeters |
| France / Spain | 105F | French bands run larger in numbering |
| Australia / NZ | 18E | AU band = US band minus 22 |
| Japan | 90F | Follows EU band sizing, cup scaling differs |
Those measurements anchor the size better than any letter, since cup letters carry different meanings across systems.
Sister Sizes For 40DDD That Fit Differently But Hold The Same Volume
Sister sizing keeps the cup volume constant while changing the band and cup letter together. For 40DDD, the immediate sister sizes are 38F (band down, cup up) and 42DD (band up, cup down).
The rule is simple: move one band size down and one cup letter up, or go one band size up and one cup letter down. Wider charts extend the family further — some listings reach 36FF and 44D — but the closer the band, the better the fit. Sister sizes rescue you when a brand runs small in the band or when your usual size is sold out. Bravissimo’s sister-size guide uses this same band-and-cup logic for its US shoppers.
Use a sister size only for the band, not the cup. If 40DDD fits your bust but feels tight around the ribs, try 42DD rather than a larger cup. If the band rides up your back, 38F pulls things back into place while keeping the same cup volume.
Why 40DDD Doesn’t Mean The Same Thing Everywhere
The letter DDD causes most of the confusion. In the US, DDD sits two steps past D. In the UK, the scale runs D, DD, E, F — so a US DDD lands at UK E. Some non-US charts label it 40F or 40E depending on the brand’s own conversion table.
A few things worth knowing before you buy:
- DDD does not mean “extra extra extra large” — it’s a cup-volume marker, not a general clothing size.
- Target’s women’s intimates chart lists 40DDD directly, as does Kohl’s Vanity Fair sizing page, so major US retailers treat it as a standard size.
Bra sizing is not fully standardized across US, UK, EU, AU, and JP systems — conversions are brand-specific guidance, not universal law. Always check the brand’s own conversion chart before ordering, and use the underbust measurement when a chart offers it.
FAQs
Is a 40DDD the same as a 40F?
In the US, no — DDD and F are different cup sizes, with F being one step larger. Outside the US, some brands label the same volume as 40F because non-US systems skip the DDD letter altogether. Check the brand’s conversion table rather than assuming the letters match your home system.
What band size is a 40DDD?
The band measures roughly 39–41 inches (99–104 cm) around the ribcage, just under the bust. The 40 refers to the stretched band length in inches, though most bras fit snugger when new. If your underbust measures closer to 38 or 42, a sister size will serve you better.
Can I wear a 38F instead of a 40DDD?
Yes, if the 40 band feels loose. A 38F holds the same cup volume as a 40DDD but with a firmer band. It’s the most common sister-size swap for this measurement, though you may need a bra extender for the first few wears if the band runs especially tight.
References & Sources
- Bravissimo. “Sister Sizes Guide.” Explains the band-and-cup sister-size logic used in this article.
- Target. “Women’s Plus Intimates Size Chart.” Lists 40DDD as a standard US size in women’s intimates.
- Kohl’s. “Vanity Fair Women’s Bras Size Chart.” Confirms 40DDD appears in major US retailer bra sizing.