US to AU conversion

40A in Australian Bra Size

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

Instant answer

40A (US) =

18A AU

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

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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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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 18A 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 40A

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

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

Sizes near 40A in Australian sizing

If 40A 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 40A and their Australian equivalents.
US size	AU size	How it differs
38A	16A	One band step snugger, same cup letter.
40B	18B	One cup step up, same band.

What this conversion means

If you searched for 40a australian size, the short answer is 18A. The full table shows the same US size across every supported system so you can compare retailer charts without opening several pages.

Sister sizes for 40A

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

What measurements make a 40A?

40A starts with the underbust, then adds cup depth from the bust measurement. In the current calculator formula, the closest starting range is about 39-41 inches (99-104 cm) under the bust and about 40.5-41.5 inches (103-105 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 40A big or small?

The label 40A can look more dramatic than it fits, especially across systems. In this size set, the US equivalent uses a fuller band and a lower 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 40A 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 40A differs between brands

Brand sizing matters for 40A because cup depth, wire width, and band stretch are design choices. 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 40A

A good shopping path for 40A starts with everyday support, then moves into outfit-specific shapes. 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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Soft Cup Edit

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FAQ

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

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

What is 40A in European sizing?

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

How do I know if 40A 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 40A?

38B are the closest sister-size options for 40A 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 40A?

The current calculator formula points to about 39-41 inches underbust and 40.5-41.5 inches bust, or roughly 99-104 cm and 103-105 cm. Treat that as a starting range and then check the real fit.