US to AU conversion

40D in Australian Bra Size

Convert 40D from US sizing to Australian sizing, with the full international table, nearby sister sizes, and fit checks in one place.

Instant answer

40D (US) =

18D AU

In this sizing table, 40D in US sizing converts to 18D in Australian sizing.

Need an Australian calculator?

If you are starting from body measurements instead of a known label, use the AU/NZ calculator with centimetres selected by default.

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Not sure about your size? Recheck your measurements before comparing conversion labels.

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Sizing varies by brand

A conversion gives you the closest label in another sizing system, but brands can grade cups, wires, and bands differently. Use the converted size as a starting point, then check the retailer's chart and the fit of the actual bra.

Before you buy in Australian sizing

Use 18D as the translated label, not as a fit guarantee.
Check the retailer's size chart because some brands grade bands and cups differently.
If the cup volume feels close but the band changes, compare sister sizes before switching cup letters.
When possible, check return rules before buying across sizing systems.

Full conversion table for 40D

40D bra size conversion across US, UK, EU, French, and Australian sizing.
US	UK	EU	FR	AU
40D	40D	90D	105D	18D

Bra sizing varies between brands. Use this as an accurate starting point and check the fit.

Sizes near 40D in Australian sizing

If 40D is close but not right, these are the neighbouring US sizes and what each one becomes in Australian sizing. Band neighbours change the fit around the ribcage; cup neighbours change volume.

US sizes adjacent to 40D and their Australian equivalents.
US size	AU size	How it differs
38D	16D	One band step snugger, same cup letter.
40C	18C	One cup step down, same band.
40DD	18DD	One cup step up, same band.

What this conversion means

This page answers the specific 40d australian size conversion using the site's shared sizing data. 18D is the Australian label for 40D here, and the table above keeps the other supported systems together for quick comparison.

Sister sizes for 40D

Sister sizes: 38DD can be worth checking when the cup volume feels close but the band needs a different feel.

What measurements make a 40D?

For 40D, the band number gives the ribcage anchor and the cup describes the bust difference. In the current calculator formula, the closest starting range is about 39-41 inches (99-104 cm) under the bust and about 43.5-44.5 inches (110-113 cm) around the fullest part of the bust. The band comes from the underbust rounding, while the cup step comes from the difference between bust and band.

Is 40D big or small?

40D sits in context only when the number and letter are read as a pair. In this size set, the US equivalent uses a fuller band and a middle cup step. Cup letters are relative to the band, so a D on one band is not the same volume as a D on every other band. The most useful question is whether the band stays level and the cups hold smoothly, not whether the label sounds large or small.

If 40D doesn't fit right

Band rides up: The band may be too loose or stretched out; try a snugger band or compare the snugger sister size.

Cups gape: The cup may be too roomy, too deep, or pulled away by a loose band; check the band before changing cup volume.

Cups spill: The cup volume may be too small or the cup shape may be too closed; try one cup step up before changing the band.

Straps dig in: The straps may be compensating for a band that is not supporting enough; reset the band fit before tightening straps.

How 40D differs between brands

A conversion points you to a label, but a brand chart tells you how that maker expects 40D to fit. A firmer elastic can make the same band feel smaller, and a shallow or narrow cup can make the same cup letter feel different. Check the retailer chart, read fit notes when available, and compare the label against the brand and region sizing guide before treating the conversion as final.

Shopping for 40D

For 40D, practical shopping is less about one perfect style and more about reading the fit quickly. If the cup is in a lower or middle step, lightly lined T-shirt styles can make gaps easy to spot. Fuller cup steps often benefit from styles with steadier side support, deeper cups, or a balconette shape depending on breast shape. For special outfits, compare the fit needs in the outfit guides before choosing a strapless, plunge, or backless option.

Bras in your size

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Everyday Fit Store

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Comfort Band Co.

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Soft Cup Edit

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FAQ

Is 40D in the US the same as Australian sizing?

Use 18D as the Australian match for 40D in this dataset. The label may look similar in some systems, but it still belongs to a different sizing sequence.

What is 40D in European sizing?

In this same table, 40D converts to 90D (EU). That helps when a retailer shows a European chart instead of a Australian one.

How do I know if 40D fits?

A good fit should feel secure without digging. Watch for a band that rides up, cups that wrinkle, or straps carrying most of the support.

What sister sizes work with 40D?

38DD are the closest sister-size options for 40D in this dataset. Try a sister size when cup volume feels close but the band needs to feel snugger or looser.

Why do bra sizes differ between countries?

Countries and brands do not all use the same band labels or cup-letter sequence. A conversion translates the closest standard label, but the final fit still depends on the specific bra.

What measurements usually make 40D?

The current calculator formula points to about 39-41 inches underbust and 43.5-44.5 inches bust, or roughly 99-104 cm and 110-113 cm. Treat that as a starting range and then check the real fit.