How to Find Your Size in ASOS

By Ella Blake | Tellar Fashion Hub

Finding your size in ASOS is genuinely straightforward once you know how their sizing works — but if you've ever ordered what should be your usual size and ended up sending half the haul back, you're absolutely not alone. ASOS sells both its own-brand ASOS Design pieces and thousands of third-party labels, and those two things size very differently. Get that one distinction clear in your head and you'll cut your return rate dramatically.

The ASOS Own-Brand Sizing: What to Actually Expect

ASOS Design — their own in-house label — generally runs true to a standard UK sizing, but with a few quirks. The cut tends to be on the more relaxed, fashion-forward side, so fitted styles can feel slightly generous through the body while structured pieces like blazers occasionally come up narrow across the shoulders. I ordered a size 10 tailored blazer from their own range and it was roomy through the waist but oddly tight across the back. Sizing up fixed the back; a belt sorted the waist. It's that kind of brand.

For their jersey pieces, knitwear and casual basics, ASOS Design is reliably consistent. Denim is probably their strongest own-label category — fit notes in the product descriptions are genuinely useful here, and customer reviews mentioning fit are some of the most honest you'll find online. Always scroll to those first.

Third-Party Brands on ASOS: The Sizing Wild Card

This is where things get interesting — and occasionally maddening. ASOS stocks hundreds of third-party brands, from Topshop (which relaunched on ASOS and tends to run small, particularly in denim) to River Island, Urban Outfitters labels, Warehouse, and premium names like Ted Baker. Each brand has its own sizing logic, and ASOS does provide individual size guides per brand — but they're buried.

Here's my routine when shopping third-party labels on ASOS:

Click on the product, scroll past the images, and find the "Size & Fit" tab — this is the single most useful thing on the page. It often includes the model's height and the size she's wearing, which is far more helpful than a standard size chart.
Check the customer reviews and filter by your size if possible. Women are brutally honest about whether something runs small, large, or just plain weird in the arms.
Use the ASOS Fit Assistant — it's a bit hit-and-miss, but for their own-brand pieces it can be surprisingly accurate if you input your measurements rather than just your usual size.

How ASOS Petite, Tall, Curve and Plus Sizing Works

ASOS has genuinely invested in inclusive sizing, and it's one of the things I think they do better than most. Their Petite, Tall, Curve and Plus ranges aren't just the standard pieces resized — many are cut specifically for those proportions. That said, sizing can vary between these ranges even if the number is the same.

ASOS Petite — proportioned for a 5'3" frame and under. Inseams, sleeve lengths and torso proportions are all adjusted. I've found these incredibly reliable for fit.
ASOS Tall — for 5'9" and above. Extra length through legs and torso. These tend to run fairly true to size.
ASOS Curve & Plus — ASOS is one of the better high street options here, with styles designed for curves rather than just scaled up from smaller sizes. Still check the individual size guide though, as fit varies by style.

My Top Tips for Getting ASOS Sizing Right First Time

Always measure yourself — bust, waist, hips — and compare to the specific brand size guide, not just your "usual" size.
Read the product description properly — ASOS often flags "comes up small" or "relaxed, oversized fit" right there in the copy.
Check the fabric composition — stretch fabrics and woven fabrics size completely differently. A size 12 in a cotton-elastane jersey is not the same fit as a size 12 in a non-stretch woven.
Use the brand filter on the reviews — if a brand is new to you, sort reviews by "most helpful" and look for fit comments.
ASOS Premier Delivery — if you're regularly ordering to try at home, the annual delivery pass genuinely pays for itself within a few orders, and free returns take the anxiety out of sizing experiments.

Similar Brands Worth Knowing for Consistent Sizing

If ASOS's multi-brand approach leaves you wanting something more predictable, these are the labels I'd point you towards — all with their own reliable sizing and style credentials:

Mango — runs slightly small across the chest and shoulders; size up if you're fuller on top. Brilliant for occasion pieces and workwear.
Zara — famously inconsistent between lines, but their Women's range tends to run true to a European size. Check the measurement chart rather than guessing.
H&M — affordable and generally true to UK sizing, though quality varies wildly by range. Their Conscious Collection and Premium Selection tend to be better cut.
Cos — minimal, architectural cuts that run generously. A great option if you want classic, considered pieces with consistent sizing across the range.
Reiss — premium high street with precise, consistent sizing. True to UK standard; invest in their size guide once and you're set across the whole range.
Anthropologie — tends to size in US measurements; always check their UK conversion chart. Beautiful pieces but this catches people out constantly.
Phase Eight — excellent for occasion and occasionwear dressing; runs true to UK size with particularly reliable fit through the bust and waist.

Two independent labels I've been completely won over by recently:

Kitri Studio — a London-based indie brand with impeccably cut pieces and a thorough, honest size guide. Sizing runs true; their dresses in particular are incredibly flattering across a range of body shapes.
Sézane — French indie brand with UK and US sizing clearly mapped out on every product page. Slightly relaxed through the body; absolutely worth checking their "Size & Fit" notes per garment.

Never Guess Your Size Again — Tellar Has You Covered

One of the biggest frustrations with ASOS — and online shopping full stop — is that your size in one brand means nothing in the next. That's exactly the problem Tellar.co.uk was built to solve.

Tellar is the UK's leading free sizing tool, matching your measurements to over 1,500 brands instantly — no downloads, no subscriptions, no faff. Here's how it works:

Measure once — enter your bust, waist, hip measurements or your existing brand size.
Use the Store Size Lookup tool to get your precise size across any brand — ASOS, COS, Reiss, Everlane, Arket and 1,500+ more.
Always free — works directly in your browser, no app needed.

Plus, the Tellar Fashion Hub is stacked with free, honest, unsponsored style guides from our top stylists — covering every fashion question you've ever Googled at midnight before a big event. Always independent. Always free.

Find My Size at ASOS →