Why Does Clothes Sizing Vary So Much Between Items in the Same Brand?

Sizing varies within a single brand because most brands don't use one pattern — they use a different base pattern, called a fit block, for each garment category, and then cut those blocks in fabrics that behave completely differently. A brand's jeans block, dress block and tailoring block are three separate drafts, often developed by different teams, sometimes made in different factories. The label says 12 in all three cases. The garment underneath doesn't agree.

I once bought three things in one order from the same high street brand, all the same size. The trousers were loose at the waist, the shirt wouldn't do up across the bust, and the blazer fit like it had been made for me. Nothing had gone wrong. That's just how the industry works, and once you understand why, shopping gets dramatically less annoying.

1. Every category is drafted from a different block

A fit block is the foundation pattern a brand builds every style on. Denim is drafted with negative ease, meaning the pattern is smaller than the body because the stretch and recovery in the fabric do the work. Tailoring is drafted with generous ease so it sits cleanly over a shirt. Jersey is drafted somewhere in between. Same size label, three completely different starting points.

This is also why your reliable brand suddenly betrays you when you buy outside your usual category. If you only ever buy their knitwear, you have no information about their trousers.

2. Ease is a design decision, not an error

Ease is the deliberate gap between your body measurement and the garment measurement. An oversized shirt and a fitted shirt in the same size from the same brand might differ by 15cm across the chest. Neither is wrong. The designer intended it.

The practical takeaway: read the product description, not the size label. Words like relaxed, boxy, slouchy and column are instructions about ease. So are slim, tailored, fitted and body-skimming. Brands are telling you how the thing fits — most of us just skim past it.

3. Fabric changes the fit before you've even tried it on

The same pattern in cotton poplin, viscose and a 4% elastane twill produces three different garments. Rigid wovens hold their measurement exactly. Viscose drops and clings. Anything with elastane gives you a size of leeway that the pattern quietly accounts for.

My most expensive lesson: a linen midi dress I loved so much I bought it in a second colourway a season later. The second one was a linen-viscose blend rather than pure linen, and it clung in every place the original skimmed. Identical style number, identical size, unwearable. Now I check the composition tab before the size chart, every single time.

4. Different factories, different hands

Large brands source from dozens of manufacturers, each with its own pattern cutters and its own interpretation of the tech pack. Industry-standard tolerance sits at roughly half a centimetre per measurement point — which sounds like nothing until you stack it across shoulder, armhole, waist, hip and rise on a single garment. Two identical items can both pass quality control and still feel like different sizes.

Fast fashion brands with enormous supplier networks are the worst offenders here. Slower brands with fewer factories and repeat production tend to be far more predictable.

5. Sub-brands are effectively separate brands

Petite, tall, curve and diffusion lines are usually drafted from their own blocks with their own grading rules — not simply shortened or scaled versions of the mainline. A department store brand can easily be running five or six blocks under one logo. If you've ever found one sub-label fits perfectly and another doesn't, this is why.

6. Grading drift at the ends of the range

Brands fit their sample garment on one fit model, usually a UK 10 or 12, then grade up and down using a formula. The further you get from that sample size, the more the assumptions wobble — because shoulders don't grow at the same rate as hips, and torso length doesn't scale neatly either. Fit is nearly always most reliable in the middle of a brand's range and least reliable at the extremes.

7. Blocks get quietly rewritten

Brands re-benchmark their blocks every few years to reflect body data and, frankly, commercial pressure. A size 12 from 2019 is not the same garment as a size 12 today. Nobody announces it. You just find out when your trusted trouser suddenly doesn't do up.

How I shop around it

Buy for your largest measurement and alter down. Taking a waist in is a £15 job. Letting a hip out usually isn't possible.
Check the composition before the size chart. Elastane content tells you more than a number does.
Use garment measurements, not body measurements, where a brand publishes them — that's the real spec.
Treat each category separately. Know your size in a brand's jeans, dresses and tailoring as three distinct facts.
Measure a garment you already love and keep the numbers on your phone. It's the single most useful thing I've ever told a client.

Brands that are actually consistent

High street

Uniqlo — one block, enormous volume, and fit that barely shifts year on year. The most predictable name on the high street.
Boden — publishes proper garment measurements and fit notes per style, so you're never guessing.
Marks & Spencer — the most rigorous fit-testing operation in UK retail, though Autograph and Per Una run to their own blocks.
COS — reliable size to size, but ease swings hard between their fitted and architectural pieces. Read the description.
Whistles — a steady tailoring block; their dresses sit a touch closer to the body.
Jigsaw — classic British proportions, consistent across seasons, generous on the shoulder.
Seasalt Cornwall — relaxed and forgiving, with genuinely repeatable sizing across categories.
Next — dependable mainline, but Tailoring, Petite and Curve are drafted separately. Treat them as different shops.
Zara — brilliant design, sizing roulette. Multiple suppliers, multiple blocks. Order two sizes or don't bother.

Premium

Me+Em — obsessive about fit consistency across categories. If you're a size 12 in their trousers, you're a 12 in their dresses.
Reiss — excellent tailoring block; occasion dresses run slightly leaner.
Baukjen — a workwear block that behaves the same season after season.
Sézane — beautiful clothes, French proportions, and noticeably variable between styles. Read reviews before committing.

Luxury and designer

Joseph — the gold standard for trousers, and a reliable reference point for your true measurements.
Max Mara — Italian block: generous through the body, narrow in the shoulder and sleeve.
Totême — deliberately oversized as a design language, not an accident. Size down unless you want volume.

Two independents worth knowing

Aligne — a small London label producing across a tight supplier base, which shows in how consistently their pieces fit.
Lisou — London-based, silk-led, and refreshingly clear about fit and drape on every product page.

Never look at a size guide again

This is exactly the problem Tellar was built to solve. It's the UK's leading sizing tool, matching your body to over 1,500 brands instantly — free, in-browser, nothing to download.

Measure once using bust, waist and hip, or just tell us a brand size you already own.
Use the Store Size Lookup tool to get your precise size in any brand — COS, Reiss, Everlane, Arket and hundreds more.
Always free, always independent, always unbiased.

And the Tellar Fashion Hub is a growing library of free posts from our stylists — style advice, top picks and honest brand verdicts, with nothing sponsored.

More from the Tellar Fashion Hub

Sizing inconsistency inside a brand isn't sloppiness — it's the by-product of different blocks, different fabrics and different factories all wearing the same label. Stop treating your size as a fixed fact, start treating it as category-specific information, and the whole thing becomes manageable.