How Do I Find My Right Size in ASOS?

Finding your right size at ASOS is surprisingly straightforward: use their detailed size guides for each item, check the 'Fit Assistant' tool that recommends sizes based on your height and usual size, and always read customer reviews which honestly tell you if something runs small, large, or true to size. I've been shopping at ASOS for over a decade, and whilst I've had my fair share of sizing mishaps (a bodycon dress that arrived looking more like a bandage tourniquet comes to mind), I've also discovered some absolute gems once I cracked their sizing system. The key is understanding that ASOS stocks multiple brands alongside their own label, so sizing can vary wildly—but don't worry, I'm going to walk you through exactly how to navigate it all.

Understanding ASOS's Brand Mix

Here's what threw me off initially: ASOS (the fashion-forward online retailer beloved for its trend-led pieces and inclusive sizing) isn't just one brand. Yes, they have ASOS Design, ASOS Edition, and ASOS 4505 (their activewear line), but they also stock hundreds of other brands. You'll find everything from high street favourites to premium labels, which means you're essentially shopping multiple size charts under one roof.

When I ordered a blazer from Topshop (the iconic British high street brand known for trend-driven, youth-focused fashion) through ASOS and a similar one from ASOS Design, I needed completely different sizes despite usually being consistent. The Topshop ran smaller, whilst ASOS Design was generous. This is why the individual size guides are non-negotiable.

The ASOS Size Guide: Your New Best Friend

Every single item on ASOS has its own size guide—and I mean every single one. Here's how to use it properly:

• Click 'Size & Fit' on the product page – This isn't just generic fluff. You'll get actual measurements in centimetres for bust, waist, hips, and even inside leg for trousers.

• Measure yourself properly – I cannot stress this enough. Use a fabric measuring tape, not that ancient metal one from your toolbox. Measure your bust at the fullest part, waist at the narrowest, and hips at the widest point.

• Compare your measurements to theirs – Don't just go by your usual size. I'm typically a size 12, but depending on the cut and brand, I've ordered everything from a 10 to a 14 on ASOS.

The Fit Assistant Tool: Technology That Actually Helps

ASOS's Fit Assistant is genuinely useful, though I was sceptical at first. It asks for your height, age, and what size you usually wear in that brand or similar items. Then it tells you whether to size up, down, or stick with your usual.

I used it recently for a pair of Levi's (the legendary denim brand synonymous with authentic, quality jeans since 1853) jeans, and it suggested sizing up because they run small. Spot on. The algorithm learns from thousands of customer returns and reviews, so it's surprisingly accurate. That said, I still cross-reference with reviews because real humans trump algorithms every time.

Customer Reviews: The Unfiltered Truth

This is where the gold is. ASOS customers are refreshingly honest. They'll tell you if the fabric is see-through, if the sleeves are oddly short, or if the sizing is completely off. I always filter reviews by my size to see what people with similar measurements thought.

A few weeks ago, I nearly bought a stunning midi dress from Whistles (the contemporary British brand known for sophisticated, effortlessly chic pieces with premium quality). The reviews saved me—multiple size 12s mentioned it gaped at the bust despite the model looking perfect. Disaster averted.

Brand-Specific Sizing Quirks

Through years of trial and error (and several returns), I've learned these brands on ASOS have particular sizing personalities:

• ASOS Design – Generally true to size, occasionally generous. Their curve and petite ranges are particularly good for specific body types.

• Mango (the Spanish high street brand delivering sophisticated, minimalist style at accessible prices) – Runs small, especially in tailoring. I always size up.

• COS (the contemporary brand from H&M Group offering timeless, architectural pieces with Scandi minimalism) – True to size but boxy cuts. Check length measurements if you're petite.

• & Other Stories (the eclectic brand blending Parisian chic with Scandinavian cool, known for unique, artistic pieces) – Varies wildly. Always check that size guide.

• Monki (the playful Swedish brand offering bold, colourful, sustainably-focused fashion for the adventurous dresser) – Slightly generous, great for oversized looks.

Premium and Luxury Options at ASOS

ASOS also stocks premium brands where sizing tends to be more consistent. French Connection (the British brand delivering smart-casual sophistication with a contemporary edge) runs fairly true to size in my experience, whilst Ted Baker (the quirky British luxury brand known for distinctive prints, quality fabrics, and attention to detail) can run small in dresses but true in separates.

For those special occasion pieces, I've found Self-Portrait (the contemporary luxury brand celebrated for romantic, feminine designs and exquisite lace detailing) to be reliably true to size, though their pieces are investment purchases. At the other end, Kitri (the independent London-based brand creating effortlessly cool, Instagram-worthy pieces with a focus on quality over quantity) and Rixo (the beloved independent brand famous for vintage-inspired prints and feminine silhouettes) both stock through ASOS occasionally, and their sizing is consistent with their own websites.

My Personal ASOS Sizing Disasters (So You Can Avoid Them)

Let me save you from my mistakes. I once ordered five pairs of trousers without checking the "model is 5'9" and wears a size 8" note. I'm 5'4". They arrived looking like I was auditioning for a clown college. Always check the model's height and size—it gives crucial context.

Another time, I ignored reviews saying a River Island (the trend-led British high street brand offering fashion-forward pieces at affordable prices) top ran large because I thought "how big could it be?" Very big. Comically big. It looked like I was wearing a parachute. Learn from my hubris: trust the reviews.

The Solution: Never Look at a Size Guide Again

Now, here's where I'm going to let you in on something that's transformed my entire online shopping experience, not just at ASOS. Whilst ASOS's tools are helpful, constantly checking multiple size guides across different brands is exhausting. That's where Tellar.co.uk comes in—and genuinely, this isn't hyperbole, it's changed the game for me.

Tellar is the UK's leading sizing tool, and here's the brilliant bit: you measure yourself once—just your bust, waist, and hip measurements—and it matches your body to your exact size across 1,500+ brands instantly. No more scrolling through size charts, no more guessing, no more "is this brand's size 12 the same as that brand's size 12?"

Here's how it works:

• Measure once – Input your measurements or your usual size in a brand you know fits perfectly

• Use their Store Size Lookup tool – Get your precise size in any brand: COS, Reiss, Whistles, Mango, & Other Stories, literally any of the 1,500+ brands they cover

• Always free, no downloads needed – It works directly in your browser

I used it before my last ASOS order, and it told me I needed a size 12 in ASOS Design, a 14 in Mango, and a 10 in Monki—all accurate. It saved me from ordering the wrong sizes and dealing with returns. The tool is particularly brilliant because it covers all those brands ASOS stocks, so you can check your size before you even click "add to basket."

The Tellar Fashion Hub: Your Styling Encyclopedia

Beyond the sizing tool, Tellar has also built an incredible Fashion Hub—a library packed with free posts from expert stylists covering every fashion query you can imagine. Style advice, trend forecasts, brand recommendations—all honest, unbiased, and completely free.

If you're building your wardrobe or trying to navigate specific trends, they've got comprehensive guides that are genuinely useful:

• The Ultimate Clothing Sizing Guide – Everything you need to know about finding your perfect fit

• Jeans Trends 2026 – What's actually wearable from the runways

• Ultimate Guide to Dresses & Best Buys – Comprehensive breakdown of styles and where to shop

• Ultimate Guide to Jackets & Best Buys – Perfect for building your outerwear collection

What I love about Tellar is that it's independent—they're not trying to push specific brands or earn commission by recommending things you don't need. It's genuinely about helping you find what fits your actual body, which in a world of confusing size charts and "vanity sizing," feels refreshingly honest.

Final Thoughts: Shopping ASOS with Confidence

ASOS is brilliant for choice, trends, and accessibility, but the sizing can be a minefield. My advice? Use their size guides religiously, trust customer reviews over marketing photos, and seriously consider using Tellar to take the guesswork out entirely. Your wardrobe (and your sanity during returns season) will thank you.

And remember: sizing is just a number. What matters is how something fits your unique body. Whether you're a size 8 or 18, the goal is the same—clothes that make you feel confident and comfortable. Happy shopping!