What Is Sizing Like at Heidi Klein?

Heidi Klein runs true to size and is sold as mix-and-match separates, so it's one of the easiest luxury swimwear brands to fit — you take your usual UK size (XS is a 6–8, S an 8–10, M a 10–12, L a 12–14, XL a 14–16) and, because tops and bottoms are bought separately, you can size up or down on either half. That separates system is the whole reason the brand has such a devoted following, and it's why I send so many of my clients its way when they've had a miserable time in supermarket two-pieces. Below I'll talk you through exactly how it fits, where it catches people out, and which other brands to look at across every budget.

How Heidi Klein Sizing Actually Fits

I've been styling women in and out of swimwear for years, and Heidi Klein is one of the few labels where I rarely have to talk anyone off the ledge in a changing room. The brand fits each design multiple times before it goes to production, and you can feel that obsessiveness when you put it on. A few honest pointers from experience:

It's true to size. Order your everyday UK size and you'll almost always be right. I'm a steady 10 and a Medium fits me exactly as I'd expect — no nasty surprises.
Tops and bottoms are separate. This is the genius bit. If you're a 10 on top and a 12 on the bottom (hello, most of us), you simply buy two sizes. No compromise, no spillage.
One-pieces run long in the body. If you're petite, take note — I'm 5'4" and a halterneck style is your friend here, because you can hoick it up to the right length. A friend of mine, who's 5'2", learnt this the hard way with a maillot that sat a touch low at the bust.
The bust is genuinely adjustable. Neck and back ties plus supportive Italian fabric mean a single size flexes across several cup sizes. It's clever engineering dressed up as a pretty bikini.
The Body range goes further. If you're a fuller cup, the dedicated Body line caters from roughly a B/C up to an F–G, with underwiring and proper structure. It's the range I point bigger-busted clients to first.

My one fashion confession: years ago I bought a gorgeous triangle bikini a size down because it was the last in a sale, convinced I'd "make it work". Reader, I did not. With Heidi Klein you never need to do that — the separates mean there's no excuse for a too-small impulse buy.

What About the Ready-to-Wear?

The kaftans, beach dresses and resort pieces follow the same XS–XL structure (XS 6–8 up to XL 14–16), but the cut varies far more than the swimwear. Floaty kaftans are forgiving and generous; the more tailored linen dresses and trousers are cut closer, so check the individual style notes. My rule: for anything bias-cut or structured, go by your waist and hip rather than guessing from a label, because resort wear lives or dies on proportion.

Where to Shop for Swimwear and Resort Wear

Heidi Klein sits firmly at the luxury end, so here's how I'd build out the rest of your holiday wardrobe across every budget — these are the brands I actually recommend based on fit and reviews, not just name recognition.

High Street

M&S — the high street's quiet swimwear hero, with proper built-in support, tummy-control panels and a huge cup range. My first stop for flattering one-pieces under £40.
Sweaty Betty — swimwear that's genuinely designed to swim in, with secure fits and sporty silhouettes for anyone who actually gets in the water.
Boden — joyful prints and clever shaping; their tummy-smoothing swimsuits get cult-level reviews every summer.
Seasalt Cornwall — relaxed, coastal cover-ups and easy beach dresses that nail the British-seaside-meets-Mediterranean look.
Hush — throw-on kaftans and beach dresses with that effortless off-duty feel; brilliant for layering over swimwear.
Monsoon — embellished kaftans and beaded beachwear when you want a bit of holiday drama without the luxury price tag.
Phase Eight — polished resort and occasion dresses that take you from beach bar to dinner.

Premium

Reiss — sleek, minimalist resort separates and clean-lined beach dresses with a grown-up, expensive-looking finish.
Me&Em — considered cuts and elevated holiday staples; their pieces are designed to flatter real bodies rather than just hangers.
Sezane — French-girl beach dresses and breezy separates with that undone Parisian charm I never tire of recommending.

Luxury & Designer

Max Mara — sculpted, architectural swimwear and beautifully tailored resort wear for a properly polished poolside look.
Ralph Lauren — timeless, classic swimwear in block colours and nautical stripes that never date — true cost-per-wear pieces.

Two Independents Worth Knowing

Form and Fold — a brilliant British label doing cup-size-specific swimwear (think D to G with real underwire support). If you love the Heidi Klein Body range, this is your next obsession.
Davy J — sustainable, recycled British swimwear with serious sculpting and compression. Sporty, sleek and built to last season after season.

The Honest Verdict

Heidi Klein is, in my view, one of the most fit-friendly luxury swimwear brands out there. True to size, adjustable, sold as separates and engineered to support — it removes almost all the guesswork that makes swimwear shopping so dreaded. Take your usual UK size, mix your halves, watch the body length on one-pieces, and you'll be very happy indeed.

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And there's the Tellar Fashion Hub: a library stacked with free posts from our top stylists. Honest. Unbiased. Independent. Always free — style advice, top picks and the best brands, with no sponsored nonsense.

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Ella Blake — Senior Fashion Stylist & Founder, Tellar.co.uk