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40D Bras

(95 products)

How a 40D should fit

The band does around 80% of the work. Fastened on the loosest hook, a 40D band should sit level around your ribcage and stay put when you raise your arms — if it rides up your back, the band is too big regardless of how the cup feels.

Sister sizes to try

  • Band loose, cup fine — try 38DD
  • Cup overflowing — try 40DD
  • Band digs in — try 42C
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The HauteFlair Edit · Updated 2026

40D Bras: A True D Cup — the Same in US, UK and EU

A 40D is the easy one to shop across borders. The band is a 40 in every system; the cup is a D in every system too. Unlike the larger full-bust cups, where the UK and US letters split apart, a D cup is written D in US, UK and EU sizing alike.

Below: exactly what 40D converts to across US, UK and EU, where the systems agree and where they eventually split, how to measure to be sure, your sister sizes, and the styles that suit a D cup.

Quick Answer

What is a 40D bra size?

A 40D bra has a 40-inch underband and a D cup — and unlike larger cups, a D is written the same across systems. A UK 40D, US 40D and EU 90D all describe the same size: a bust roughly 4 inches larger than the band (around 44 inches around the fullest point). D is the last cup where US and UK sizing agree — from DDD up they split — which makes it the simplest full-cup size to buy across borders. Sister sizes, holding the same cup volume, are 38DD and 42C. Shop 40D bras in t-shirt, plunge, strapless, sports and full-figure styles.

D = D = DSame letter in US, UK & EU
Band 40, cup D40 inches around the ribcage
≈ 4 inchesBust minus band at this cup
US & UK agreeThey split at DDD, not D
Shop by style
All 40D Bras T-Shirt Bras Strapless Sports Bras Full Figure Minimizer All Bras

How to choose a bra at 40D

A D cup is well-supported by most well-made bras — but these five checks still decide whether it fits cleanly or shifts through the day.

What to check What good looks like Why it matters
Band fit Level all the way around, snug on the loosest hook, two fingers under it and no more The band carries most of the support at any cup — a band that rides up shifts the load onto your shoulders
Cup shape Moulded for a smooth line, or seamed for lift and projection — both work well at a D A D is served by almost every construction; pick by the shape you want under clothes, not by necessity
Underwire Wires that sit flat on the ribcage and encircle the breast without poking the underarm A wire that rides up onto tissue means the cup is a touch small, not that the style is wrong
Straps Adjustable, comfortable, staying put without being cranked tight At a D, standard straps are usually enough; if they dig, the band is likely too loose
Gore & wings Centre gore flat to the breastbone; wings tall enough to sit smooth against the side A floating gore means the cup is too small; smooth wings stop any side spillage

40D in US, UK, EU and beyond

The same body, seven labels — and at a D cup the letter barely moves. The band number changes system to system; the cup stays D.

System Size How it's written
UK 40D The size on this page — the same letter everywhere
US 40D US and UK both write a 4-inch cup as D
EU 90D Band in centimetres; US 40 = EU 90. Cup still D
France / Spain 105D EU band plus 15 — same D cup, bigger number
Italy 5D Italy numbers bands; EU 90 = Italian 5
Australia / NZ 18D Numeric band (US 40 = AU 18), same D cup
Japan 90D EU band; Japanese cups run small, so size up one cup

So is a US D the same as a UK D? Yes — at the D cup they're identical, both meaning a bust about 4 inches larger than the band. The two systems only split higher up: a UK DD is still a US DD, but a UK E is a US DDD, and a UK F is a US G. D is the last size that reads the same in both. See our full bra size conversion guide.

Find your 40D bra

Pick the card that matches what you need it for — then tap through to shop.

01

Everyday, under everything

A moulded t-shirt bra: smooth under knit, rounded shape, no seam showing through.

Shop t-shirt bras →
02

Lift and shape

A balconette or seamed cup lifts a D and opens the neckline — the going-out category at this size.

Shop all bras →
03

Running, lifting, moving

Encapsulation or a firm compression crop both work at a D. Pick by impact level.

Shop sports bras →
04

Strapless that stays

A D is very wearable strapless — look for a firm band and silicone grip and it holds.

Shop strapless →
05

Smooth the line

A minimizer redistributes for a cleaner profile under a fitted blouse without losing support.

Shop minimizers →
06

Not sure it's your size?

If your current 40D gapes or the gore floats, the conversion or your measurements may be off. Start here.

Convert my size →

The band does the lifting; the straps only steady it. A D cup is easy to fit well once the band is right — the gaping, the ride-up and the digging usually trace back to the band, not the cup.

The HauteFlair Standard

The complete 40D sizing guide

Measuring, where the systems agree, sister sizes, the fit tells and the vocabulary.

01How to measure for a 40D at home+

Two measurements, taken in a soft unpadded bra or none at all, tape level:

  • Band: snug around the ribcage directly under the bust. A 40 band comes from an underbust near 39–41 inches.
  • Bust: around the fullest point, tape parallel to the floor, not pulled tight. At 40D that lands around 44 inches.
  • Cup: subtract band from bust. A 4-inch difference is a D; 3 inches is a C, 5 a DD.

The result is a starting size, not a verdict. Cut varies mill to mill, so let the fit checks below decide — and if you're on the line between letters, try the size plus its sister sizes.

02Where US and UK sizing agree — and where they split+

A D is the crossover cup: the last one both systems write identically. Here's the ladder:

  • They agree through DD: A, B, C, D, DD read the same in US and UK. A 40D is a 40D in both.
  • They split at DDD: above DD the US stacks another D (DDD) while the UK moves to E — so a UK E is a US DDD.
  • From there they diverge: UK F is a US G, UK FF is a US H, and so on up the alphabet.

So a D cup is the one you never have to convert. Above it, always check whether a chart is UK or US before trusting the letter.

03Sister sizes: 38DD, 40D, 42C+

Cup volume moves with the band, so 40D has neighbours holding roughly the same cup:

  • Down a band, up a cup: 38DD — for a firmer band that feels tighter.
  • Up a band, down a cup: 42C — for a looser band with the same cup room.

Reach for a sister size when the cup fits but the band doesn't, or when your exact size is out of stock in a style you want. What you should never do is loosen the band to fix the cup — that hands the support to your shoulders. The full logic is in our sister sizes guide.

04The five fit tells at a D cup+

Stand at a mirror. In order of usefulness:

  • Band riding up at the back — band too loose. Go down a band, up a cup (your sister size).
  • Gore floating off the breastbone — cup too small, or the wire is too narrow for you.
  • Spillage at the top, underarm or under the wire — cup too small. Not a shape problem.
  • Wrinkling or gaping at the top of the cup — cup too big, or the wrong style for your shape.
  • Straps digging — you've tightened them to cover for a loose band. Fix the band first.

Check on the loosest hook when the bra is new; you move to the tighter hooks as the elastic relaxes over time.

0540D, D cup, 90D: the vocabulary+
  • 40D — a 40 band with a D cup; the same in US and UK sizing.
  • EU 90D — the same body; 90 is the band in centimetres, and the cup is still D.
  • Standard vs full bust — a D sits at the crossover: the top of the standard range and the start of the full-bust range, so it's stocked in both kinds of bra.
  • Sister size — a different band-and-cup pairing holding the same cup volume; 40D's are 38DD and 42C.
  • The split — above DD, US and UK letters diverge (UK E = US DDD). At D they still match.

40D bras FAQ

The questions shoppers ask most, answered straight.

What is a 40D bra size?

A 40D has a 40-inch underband and a D cup. In US, UK and EU sizing a D cup is written the same way — it's a bust about 4 inches larger than the band (around 44 inches around the fullest point), which makes 40D a US 40D, a UK 40D and an EU 90D. It's a mainstream cup, at the point where standard and full-bust ranges meet.

Is 40D a big bra size?

Not especially — D is one of the most commonly sold cups, and the letter alone doesn't settle it. Cup volume is measured against the band, so a 40D holds more than a 38D (smaller band) and less than a 42D (larger band) even though all three read D. The band is half the size. A D is the crossover point: the top of the standard range and the start of the full-bust range.

Is 40D a UK or US size?

Either — at the D cup it's the same. US and UK sizing agree all the way up to DD, so a UK 40D and a US 40D are identical. The two systems only split higher up: a UK E is a US DDD, and a UK F is a US G. D is the last easy one to shop across borders.

What is a 40D in US sizing?

Also 40D. A 4-inch difference between bust and band is a D cup in both US and UK sizing, so the letter doesn't change. This is different from larger UK cups (FF, GG) that get rewritten in US letters — a D stays a D.

What is a 40D in EU sizing?

A 40D is an EU 90D. The band converts from inches to centimetres (40 inches = EU 90), but the cup letter stays D — the D cup is one of the few that lands on the same letter in US, UK and EU sizing. In France or Spain the same size reads 105D.

Is a 40D bigger than a 40C?

Yes, by one cup. On the same 40 band, each step up the alphabet adds cup volume, so a 40D is one cup larger than a 40C and one cup smaller than a 40DD. If a C gapes at the top or a DD spills over, D is the size in between.

What's the difference between 40D and 40DD?

One cup. A DD (a US and UK DD alike) holds about an inch more projection than a D on the same band. If your 40D cup cuts in, spills over the top or the underarm, the next size up is 40DD — not a bigger band.

What are the sister sizes for 40D?

38DD and 42C — the same cup volume on a different band. Drop to 38DD for a firmer band, move up to 42C for a looser one. Use a sister size when the cup fits but the band doesn't, or when your size is sold out in the style you want.

How do I measure for a 40D at home?

Measure snugly around your ribcage under the bust for the band, then around the fullest point with the tape level. Subtract the first from the second: a 4-inch difference on a 40 band points to a D cup. Treat it as a starting size and let the fit checks decide.

What bra styles work best for a 40D?

Almost anything — D is a well-served cup, so t-shirt, plunge, balconette, strapless and sports styles all come in it. Look for a firm band and a supportive cup; a moulded t-shirt bra works smoothly under knits, and a balconette lifts and shapes for a rounder neckline.

Sizing guidance here is general. Bra sizing is not standardised — cup labelling, wire shape and band firmness vary by brand and style, so conversions are a starting point, not a guarantee. Always check the individual brand's size chart and treat any measurement as a place to begin. Size availability reflects current stock. Last reviewed August 2026.

Shop 40D bras

A D cup that reads the same in US, UK and EU — in t-shirt, plunge, strapless, sports and full-figure styles, with firm bands and cups that hold their shape.

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