How Do Brands Decide on Their Sizing?

Brands decide their own sizing entirely in-house, because there is no legal standard forcing them to do anything else — a size 12 is whatever a brand's design team says a size 12 is, and that decision usually starts with one real woman standing in a studio being measured. The British Standards Institution publishes guidance, but retailers are under no obligation to follow it. That single fact explains almost every frustrating fitting-room moment you have ever had.

I've spent years watching clients blame their bodies for something that is, quite honestly, a business decision made in a design meeting. So let me pull the curtain back properly.

It Starts With a Fit Model, Not a Formula

Every brand builds its sizing around a base block — a master pattern for one middle-of-the-range size, usually a UK 10 or 12. That block isn't drafted from some neutral, universal average. It's drafted around a specific human being: the brand's fit model, chosen because her proportions reflect the customer they want to dress.

And here's the bit almost nobody outside the industry knows: professional fit models are known by name within the trade. Their measurements sit on file at dress-form companies. A design team can effectively order a mannequin shaped like a particular woman, because she is the body their whole range is built on.

So if a brand's fit model happens to be long in the waist and narrow through the hip, that assumption is baked into every single garment they will ever sell — in every size. If she's shorter-waisted with a fuller hip, that becomes the blueprint instead. You aren't imagining it when one high street shop just works on you and another never does. You're simply closer to one brand's fit model than the other's.

Then Comes Grading — And This Is Where It Gets Messy

Once the base block is signed off, every other size is created by grading: adding or subtracting set amounts at the bust, waist, hip, shoulder, armhole and length. The amount added at each point is called the grade increment, and — crucially — each brand writes its own grade rules.

Two brands can start from an identical size 12 and produce wildly different size 18s, because:

• Bodies don't scale evenly. Shoulders barely change between sizes; bust and hip change a lot. Lazy grading just inflates everything equally, which is why some larger sizes come out with cavernous armholes and drooping shoulder seams.

• Length is often forgotten. Good grading adds rise, sleeve and body length as sizes increase. Cheaper grading doesn't, which is why a size 20 top can feel oddly cropped.

• Extended sizes need re-engineering, not stretching. Brands that genuinely commit to a wide range redraft the block for their largest sizes rather than photocopying the proportions upwards.

This is precisely why a brand can be brilliant on you at one end of its range and hopeless at the other.

The Target Customer Decision

Before a single pattern is cut, a brand decides who it is dressing — and that shapes the numbers on the label. A youth-led label drafts for a straighter, shorter-waisted frame. A brand aimed at women over forty typically drafts with a fuller bust, a softer waist and more room through the upper arm. Occasionwear tends to run snug because it's designed to be structured; loungewear runs generous because comfort sells it.

None of this is written on the swing tag. It's all invisible, and it's all deliberate.

Vanity Sizing: The Uncomfortable Bit

Then there's size inflation. The last publicly available UK sizing survey before the modern era took place in 1952, when the standard woman was a size 12. Bodies have changed since — but so have labels, and not always honestly. What was once cut as a 14 is frequently sold as a 12, because retailers know perfectly well that customers feel better buying the smaller number.

A 2011 UK study found misleading size labelling on more than half the garments it checked. Investigations since have found size 10 skirts with waistlines that measure closer to a 16. Some brands lean into it hard. Others resist it entirely and get accused of "running small" when actually they're just being accurate. Neither approach is regulated.

Why Brands Don't Simply Agree on a Standard

You'd think they'd fix it. But there's a genuine counter-argument from within the industry: if every brand sized identically, women whose shape sits outside that standard would have nowhere to go. The variation, frustrating as it is, means there's usually some brand out there cut for your proportions. The problem isn't that variation exists — it's that shoppers are given no map to navigate it.

My Own Wins and Fails

My worst: a beautiful navy tailored jacket bought in my "usual" 12 from a label I'd never tried, for a client presentation. I couldn't lift my arms above shoulder height. Their fit model was clearly narrower through the back than I am, and no amount of wishful thinking fixed it. I presented that day with my arms welded to my sides.

My best: discovering, entirely by accident, that one particular brand's trousers fit me straight off the rail with zero alterations — because their block happens to be drafted with a longer rise. I've bought the same style in four colours since. That's not loyalty. That's just finding the brand whose fit model shares my shape.

What This Means For You

• Stop treating your size as fixed. It's a label, not an identity. Expect to move across two or three sizes depending on the brand.

• Learn your four measurements — bust, waist, hip and inside leg — and check them against the brand's own chart rather than the number you assume you are.

• Identify your "block brands." Once you find a label whose base block suits you, stay with it. Their whole range is built on the same foundation.

• Read the fit intent. "Relaxed," "tailored" and "true to size" are drafting instructions, not marketing fluff.

• Ignore vanity sizing entirely. The number is the least reliable piece of information on the garment.

Brands Worth Knowing For Consistent, Honest Fit

High Street

These are the accessible labels whose sizing I find genuinely dependable across a range, rather than only at the sample end: Uniqlo (rigorous, engineering-led fit and clearly published measurements), Warehouse, Oliver Bonas, & Other Stories, Monsoon, John Lewis ANYDAY, Albaray and Nobody's Child. All of them publish body measurements rather than vague garment guesses, which matters more than any of them will ever tell you.

Premium

Baukjen grades thoughtfully across a genuinely wide range. L.K.Bennett holds a consistent block year on year, which makes repeat buying low-risk. Ghost London is worth knowing if you sit between sizes, as their fluid cuts are far more forgiving of a non-standard hip-to-waist ratio.

Luxury

Joseph drafts precise, narrow tailoring — superb if that's your shape, unforgiving if it isn't. Toteme runs deliberately relaxed and generous through the body, so size down before you assume anything.

Two Independents Worth Your Attention

Aligne is a London label doing intelligent, slightly oversized tailoring with unusually honest fit notes on each product page. Damson Madder is the British indie I recommend most often to clients who feel let down by high street grading — the pieces are playful, but the sizing is drafted with real care across the full range.

Find Your Perfect Fit — In Any Brand

Now you know how brands set their sizes, here's the sensible next step: stop guessing. Tellar exists to translate your measurements into your actual size at any shop you like.

No more size guide guesswork. No more disappointing deliveries. No more fitting room frustration.

• Works instantly in your browser — no app, no download needed

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Use the Store Size Lookup tool to get your precise size in any brand — whether that's Uniqlo, Warehouse, Joseph, Toteme, or anything in between. It takes about thirty seconds and will save you hours of uncertainty.

Find Your Size Now

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