UK to US conversion

UK 40D in US Bra Size

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

Instant answer

40D (UK) =

40D US

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

Full conversion table for 40D (US 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.

What this conversion means

Reverse conversions are useful when a tag, retailer, or size chart starts outside the US system. In this table, UK 40D converts to US 40D, then the adjacent links help you compare nearby options.

Sister sizes for the US equivalent (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?

A size like 40D makes more sense when the two tape measurements are shown side by side. 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. This page uses 40D as the US equivalent for those measurement notes.

Is 40D big or small?

40D should be treated as a fit label, not as a judgement about body size. 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

Use 40D as the starting label, then let the individual brand chart narrow the choice. 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

Treat 40D as your anchor size while you compare cup shape, strap placement, and band feel. 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

Looking for 40D? We may earn a commission if you buy through sponsored links.

Everyday Fit Store

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

→

Comfort Band Co.

Placeholder for supportive everyday styles by band and cup.

→

Soft Cup Edit

Placeholder for wire-free and lounge options.

→

FAQ

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

In this dataset, 40D (UK) converts to 40D in US sizing. Some brands publish their own charts, so use this as the closest standard label and still check the real fit.

What is 40D in French sizing?

40D (UK) matches the same base record as 105D (FR). The full table on this page shows each supported label side by side.

How do I check the fit of 40D?

Start with the band: it should feel firm and even around your ribcage. Then check cup containment, wire comfort, and whether the center gore lies close on wired styles.

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?

Bra labels are written differently across US, UK, EU, French, and Australian systems. Cup letters can also diverge after D, so a converted label is a starting point rather than a promise of identical fit.

What measurements usually make 40D?

40D maps to US 40D here. 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.