US to UK conversion

40A in UK Bra Size

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

Instant answer

40A (US) =

40A UK

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

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 UK sizing

Use 40A 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 UK sizing

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

US sizes adjacent to 40A and their UK equivalents.
US size	UK size	How it differs
38A	38A	One band step snugger, same cup letter.
40B	40B	One cup step up, same band.

What this conversion means

This page answers the specific 40a in uk conversion using the site's shared sizing data. 40A is the UK label for 40A here, and the table above keeps the other supported systems together for quick comparison.

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 is built from a band measurement and a bust measurement, not from the label alone. 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?

40A is not automatically big or small; it depends on the band and the cup together. 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

Two brands can print 40A or its equivalent on the tag and still cut the bra differently. 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

When shopping for 40A, start with styles that make the band easy to judge. 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

Placeholder for a broad size range and return-friendly basics.

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Comfort Band Co.

Placeholder for supportive everyday styles by band and cup.

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Soft Cup Edit

Placeholder for wire-free and lounge options.

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FAQ

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

Use 40A as the UK 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 French sizing?

In this same table, 40A converts to 105A (FR). That helps when a retailer shows a French chart instead of a UK 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.