What Is Sizing Like At Decathlon?

By Ella Blake – Senior Fashion Stylist & Founder | Tellar – Always honest, unbiased, & unsponsored post

Decathlon runs small, so for most of its ranges I’d size up – especially in tops, base layers and sports bras, because the house cut is athletic and close to the body rather than relaxed. That’s the headline, and after years of dressing clients for everything from a first 5k to a ski week, I want to save you the returns queue. The thing that catches people out is that Decathlon isn’t one brand with one fit; it’s a French value giant that designs under a dozen or so in-house labels, each with its own design team. Get your head around that and the whole place suddenly makes sense.

Why Decathlon sizing trips people up

When you buy from Decathlon you’re really buying from its “passion brands” – Domyos for gym, yoga and dance, Kalenji for running, Quechua and Forclaz for hiking and trekking, Kipsta for team sports, Nabaiji for swimming and Van Rysel for road cycling. Because separate teams design each one, a medium in a Domyos legging will not necessarily match a medium in a Quechua fleece. So the golden rule isn’t “I’m a Decathlon medium” – it’s “check the fit per range every time.”

The cut is European and sporty – trim through the chest, waist and arms, designed to move with you, not drape over you.
Labelling varies – some pieces use S/M/L, others EU numeric sizing, so always glance at the on-product size guide rather than guessing.
Returns are generous – you get a long returns window, so if you’re between sizes, order both and send one back.

The garment-by-garment lowdown

Leggings and gym bottoms

This is where Decathlon genuinely shines. The Domyos high-waisted leggings fit true to size and squat-proof, with a compressive, hold-you-in feel that punches well above their price. I bought a pair years ago purely to test them for a client, fully expecting to bin them, and they’ve quietly become the most-worn thing in my gym drawer. If you like a looser fit, size up one; otherwise stick to your usual.

Tops, base layers and sports bras

Here’s where I’d almost always go up. Kalenji running tops and the merino base layers run small and snug – my first Kalenji tee in my normal size was practically painted on, and a size up was perfect. Sports bras (Domyos and Kalenji) run small too, so size up and check the band rather than trusting the cup letter alone.

Fleeces, jackets and outdoor kit

Quechua and Forclaz are cut more generously, occasionally with a slightly boxy, unisex-leaning shape. The cult MH100 fleece and the puffer jackets are roomier, so your usual size – or even a size down if you want a neater line – tends to work. These are the Decathlon buys fashion editors quietly love.

Footwear

Trainers are largely true to size, though for longer runs in the Kiprun range I’d nudge up half a size to allow for swelling. Quechua walking boots run narrow, so if you have a wider foot, try before you commit to a hike in them.

My honest take as a stylist

Decathlon is a high-low styling goldmine. The trick is to use it for technical basics – plain black leggings, merino layers, a packable puffer – and let your hero pieces do the talking elsewhere. A 365-day returns policy means there’s no excuse for keeping something that doesn’t fit, so be ruthless. Buy two sizes, keep the winner, send the rest back.

Where else to shop for activewear

If you love the value but want a little more polish or range variety, here’s where I’d send my clients.

High street

M&S – the Goodmove range is the quiet hero of affordable activewear, genuinely supportive and consistently sized.
H&M – H&M Move delivers trend-led, low-commitment pieces; sizing is fairly true so order your usual.
Next – the Active line is brilliant for family-friendly, no-fuss kit at a fair price.
Superdry – the place to go for sporty off-duty layers, hoodies and joggers with a roomier, casual cut.

Premium

Sweaty Betty – the British benchmark for studio-to-street leggings; the sculpting fabrics and supportive fit justify the price.
Lululemon – cult Align leggings and a buttery handfeel; sizing runs slightly small, so size up if you’re between.
Gymshark – sharp, body-skimming gym wear with serious squat-proof credentials and a younger, trend-driven feel.

Luxury

Max Mara Leisure – for elevated athleisure that crosses over into off-duty dressing; impeccable fabric and that quietly expensive look.

A couple off the beaten track

Adanola – the cult British label that nailed the minimal, everyday-luxe activewear look at a fraction of designer prices; fits true to size.
Finisterre – a Cornish, B-Corp outdoor brand born from cold-water surfing, perfect if you want your Quechua-style outdoor kit with real sustainability behind it.

Stop guessing your size altogether

This is exactly the headache I built Tellar.co.uk to fix. It’s the UK’s leading free sizing tool – match your body to 1,500-plus brands instantly, so you never squint at a size guide again.

Measure once – using bust, waist and hip, or just an existing brand size you already trust.
Use the Store Size Lookup tool to get your precise size in any brand – COS, Reiss, Everlane, Arket and more.
Always free, no downloads needed – it works straight in your browser.

There’s also the Tellar Fashion Hub: a library stacked with free posts from our top stylists. Honest, unbiased, independent and always free – style advice, top picks and the best brands for every body.

Find your perfect size in seconds

Tellar.co.uk is the UK’s leading free sizing tool – match your exact measurements to your perfect size in 1,500+ brands instantly. No conversions, no guesswork, no returns.

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