What Is Sizing Like at Speedo? Everything You Need to Know Before You Buy

By Ella Blake — Senior Fashion Stylist & Founder | Tellar

ALWAYS HONEST, UNBIASED & UNSPONSORED

Speedo sizing runs small — particularly in their performance and competitive swimwear — and if you order your usual UK size without checking, there is a very real chance you will end up in something that fits more like a second skin than a swimsuit. I have made that mistake personally. A few years back, I confidently picked up a Speedo one-piece in my standard size for a holiday and spent the entire trip quietly tugging at it. Lesson learned. Size up, and size up confidently.

That said, Speedo is genuinely brilliant at what it does. As the world's leading performance swimwear brand, the engineering behind their fabrics is exceptional — chlorine-resistant, shape-retaining, supportive — and once you crack the sizing, they are incredibly reliable. Let me break it all down properly.

Why Does Speedo Run Small?

It comes down to purpose. Speedo was built for competitive swimmers, and competitive swimwear is designed to sit close — very close — to the body to reduce drag in the water. The closer the fit, the less fabric billowing around you as you swim. For leisure swimmers and beachgoers, that performance cut can feel uncomfortably tight if you order your typical size.

Speedo's sizing is based on UK measurements, which is helpful, but their actual garment dimensions are cut narrower and shorter than most UK high street brands. Think of it a bit like buying sportswear versus everyday clothing — a sports bra fits very differently to a regular bra, even in the same size.

Swimsuits & One-Pieces — Go Up at Least One Size

This is where the sizing difference is most noticeable. Speedo's one-pieces — from their classic Endurance+ range through to their more stylish leisure styles — are consistently cut snugly. I recommend going up one full size as a baseline, and if you carry any weight through the hips or bust, go up two.

Endurance+ range: their most compressive fit — built for lap swimmers. If you swim regularly, this tightness is actually brilliant for support. But do not be alarmed by how it feels in the changing room. It should feel firm, not cutting off circulation.
Boom Allover range: still performance-focused but slightly more relaxed in cut — still worth sizing up by one.
Printed leisure styles: Speedo's more casual, holiday-ready one-pieces tend to be slightly more generous, but I would still size up by one as a precaution.

A quick tip: when trying on a Speedo swimsuit, sit down, stretch your arms overhead, and try a few swimming arm movements. If it pulls uncomfortably across the shoulders or the gusset rides up too much, go up again.

Bikinis — Tops & Bottoms Sized Separately

Speedo's bikini range is more limited than their one-pieces — they lean performance over style here — but the same sizing principles apply. The bottoms are typically cut high-legged and athletic, which is flattering if that is your aesthetic, but can feel quite firm through the hip.

Bikini tops: size up by one from your usual bra size as a starting point. If you are a larger cup size, you may find the range limited — Speedo's bikinis are not designed with significant bust support in mind.
Bikini bottoms: size up by one from your usual bottoms size. The leg cut can make them feel smaller than they actually are.

Honestly? If swimwear fashion — prints, styles, cover-up coordinates — is your priority for a holiday, Speedo is not the brand I would reach for first. Their strength is function. For style, there are brilliant alternatives below.

Rash Guards, Sports Tops & Swim Shorts

Speedo's rash guards and swim shorts follow standard UK sizing much more closely than their swimsuits. Their rash guards in particular are a brilliant buy — excellent sun protection, incredibly durable, and the sizing here is actually pretty true to size. I would still suggest checking the specific product's measurements if you are between sizes, but you will not need the dramatic size-up you would with a swimsuit.

Rash guards: true to size, or size up one if you prefer a looser fit for comfort over performance.
Swim shorts: true to size with a comfortable fit — their built-in mesh briefs are a thoughtful feature.
Swim leggings: size up one — these are cut performance-close like the swimsuits.

My Top Sizing Tips for Speedo

Always check the specific product's size guide on their website — not all ranges are cut the same.
When in doubt between two sizes, go up.
If you are buying online, order two sizes and return the one that does not fit.
For performance lane swimming, embrace the snug fit — it does genuinely improve your feel in the water.
Use Tellar's Store Size Lookup tool — it maps your measurements directly to Speedo's size range so you are not guessing.

High Street Alternatives for Swimwear

If Speedo's athletic, performance-led aesthetic is not quite what you are after — or you want a broader range of styles and more generous sizing — here are my top high street picks for swimwear. These all do brilliant one-pieces, bikinis, and holiday cover-ups, and their sizing is generally far more forgiving than Speedo's.

🏖️ HIGH STREET PICKS

M&S — My go-to for swimwear that actually fits properly. M&S do excellent non-wired swimsuits with brilliant tummy-control options, and their sizing is reliably generous. Particularly good for D+ cup sizes.
Boden — Joyful prints, brilliant quality, and they size inclusively. Their swimsuits come in long-length options too, which is a lifesaver if you are tall. One of the best high street swimwear ranges, full stop.
Next — Consistently strong swimwear at sensible prices. Great for families with a wide range across ages, and their own-brand one-pieces are sturdy and hold their shape well after chlorine.
ASOS — Enormous range covering every swimwear style imaginable, with really strong curve and petite options. Great for trend-led buying, especially at the price point.
Sweaty Betty — Brilliant for active swimwear with a fashion edge. Their swimsuits are designed for real movement, sizing is true to UK sizes, and the fabrics are excellent.
Fat Face — Relaxed, beach-ready swimwear with a very wearable laid-back British aesthetic. Sizes are generous and their prints feel genuinely summery without trying too hard.
H&M — Affordable, on-trend, and surprisingly decent quality for the price. Worth buying here when you want fashion-forward colours and prints without a big spend. Size up one in their bikini bottoms.
Zara — When Zara does swimwear, it does it well. Very stylish, minimal, and with strong silhouettes. Sizing here tends to run slightly small as well — size up one from your usual Zara size.

Premium Swimwear Alternatives

✦ PREMIUM PICKS

Seafolly — Australian brand with a brilliant UK presence. Their swimwear is stylish, functional, and very well made. Sizing is generous and consistent — they do genuinely great one-pieces and bikinis for all body types.
Heidi Klein — A favourite of mine for premium holiday dressing. Excellent swimsuits and cover-ups, thoughtfully designed for women who want style and quality in equal measure. Sizing is reliable and runs true to UK.
Melissa Odabash — Trusted by editors and stylists alike for a reason. Gorgeous designs, exceptional fabrics, and her swimwear actually fits beautifully. Not cheap, but worth every penny if you want it to last.

Luxury & Designer Swimwear

◆ LUXURY PICKS

Eres — The swimwear brand designers actually buy for themselves. French, incredibly refined, and genuinely flattering on every body shape. Their sizing runs small by European standards — always go up one.
Zimmermann — If you want swimwear that turns heads at the pool, Zimmermann. Their prints are extraordinary, the craftsmanship is exceptional, and the quality is investment-grade.
Hunza G — Technically now mainstream, but their crinkle fabric is so clever that it stretches to fit almost any body, making sizing a near non-issue. A genuinely genius product.

Independent & Niche Brands Worth Knowing

🌊 INDEPENDENT PICKS

Davy J — A small, sustainable British swimwear brand making beautifully constructed one-pieces and bikinis from recycled ocean plastic. Extraordinary craftsmanship, brilliant sizing guides, and a brand whose ethics match its aesthetics. One to know.
Fisch — London-based luxury swimwear brand with an incredibly chic minimal aesthetic. Their pieces are timeless, impeccably made, and their sizing is thoughtfully inclusive. If you want something truly special and a bit under the radar, this is it.

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