Bodies have changed. Our sizing blocks and grading systems have not caught up
This is the second half of the write up I promised Rachel Sheila Kan from the Real Circularity Summit, and it is the discussion that had the deepest impact on me. It came from a session called the Tru-Size Roundtable, run by Julia Reynolds, founder of Rey House and its technology arm, Tru-Size, and before that the founder of Tesco's F&F clothing brand.
Julia's starting point was a suspicion she has carried for years: the fashion industry's standard sizing blocks, the base shapes that entire grading systems are built around, were set decades ago and have quietly stopped matching real bodies. Diet and lifestyle have shifted average body composition over that time. More recently, weight loss drugs have added a sharper, faster driver, reshaping bodies unevenly through muscle loss as well as fat loss, in ways no existing size chart has any mechanism to track. Bernstein has estimated this could move up to 13 billion US dollars a year in US apparel spend as millions of people change size, with up to 5 billion dollars of existing inventory misaligned to demand, and around 80% of GLP-1 users expecting to need a new wardrobe. The UK has almost no equivalent data yet.
Julia did not just describe the problem, she proved it. She put up two avatars side by side: one built from the UK's current standard sizing base block, the shape most retailers still design against, and one built from her own scanning data, combined with data Kantar shared with her, showing the true shape of real customers, in this case women over forty. The visual difference between the two was obvious, immediately, to everyone around the table. Around a dozen industry people were there, including Julia Redman, a fashion buying and sourcing lecturer at London College of Fashion with more than thirty years as a buyer. Everyone around that table agreed on what the data showed, and agreed on what needed to change. Julia Redman spoke about how genuinely interested her own students are in fit as a subject, which struck me as a good sign: the next generation of buyers and designers coming through are already primed to care about exactly this problem.
There was a second flaw underneath the first, and it was new to me. The old assumption in grading has always been that a petite customer needs her whole body graded down proportionally, smaller everywhere by the same amount. Julia's data says that is not how real bodies actually vary. Some parts do not shrink in step with others, so a uniform petite grade is quietly mis sizing people in specific, identifiable ways that nobody had properly measured before.
The cost of getting this wrong is not abstract. Poor fit means a customer either does not buy in a changing room, because, in Julia's words, nothing does much for your self esteem quite like something not looking right on you, or she orders online and returns it, which is the same problem wearing a different coat. Once an item has been returned twice or more, the cost of processing that return genuinely decimates the buying margin on it. That return risk pushes customers to order more than one size just in case, which adds further logistics cost and carbon footprint on top. And even the item a customer keeps may go unworn if the fit is not quite right, eventually resold, donated, or in the worst case, thrown away. Waste, carbon footprint, direct cost, and a customer who does not feel great about your brand, all from the same root cause.
The flip side is the whole reason to care. A retailer that properly scans its actual customers and corrects its base blocks and grading gets better conversion in store, because people look better in the clothes and buy them. Fewer returns. Less stock left over at the end of a season, and less markdown as a result. Less product heading to landfill because nobody could wear it properly in the first place. And when someone is told they look great and asks where it is from, that is the best organic marketing a brand can get, better than anything money can buy directly. Julia has started this research with one segment, women over forty, but nothing about the method is specific to that group. It generalises to any retailer, and any customer.
Which is exactly where my own mind went sitting at that table. The majority of UK retailers and brands still delineate children's clothing by age. I checked rather than assumed this, across the full spread of the market, value to high street, and it holds. It has never made sense to me, because children of the same age can be wildly different sizes, and a single age label cannot possibly capture that. The same scanning approach that Julia is proving out for adult fit could do exactly the same job for kidswear: give retailers real evidence for how to build blocks and gradings around actual children's bodies, and just as importantly, how to name and define each size properly, so a parent can tell what they are actually buying, in store and online, rather than guessing from an age number that may or may not fit. The European approach already points a direction here: sizing by body measurement in centimetres, under the EN 13402 standard, is already the de facto standard for children's clothing across most of Europe. The UK is the outlier still leaning on age.
This is not a hypothetical switch, and I went and checked. I pulled up the exact same H&M sweatshirt on the UK site and the German site. In the UK, it is sold as 8-10Y, with the centimetre measurements tucked away behind a separate size guide link. In Germany, the same garment is sold as 134/140 (8-10Y), the centimetre range leading, age in brackets as the translation. Same retailer, same product, reversed convention by market, and it clearly costs them nothing operationally to run both. Zara's UK site shows a similar pattern, its own category pages are titled things like '4 Years | 104 Cm', age first for younger children, but from around age nine upward, Zara drops age labelling altogether and sizes purely by height in centimetres. The underlying size code was a measurement all along, age was only ever the translation layer for parents who had not yet learned to measure. There is no reason a UK brand could not do exactly the same, both a low risk step for customers here and a genuine head start if you ever sell into Europe, where a size chart already speaking centimetres is simply speaking the local language.
The other piece of customer education worth building into any size chart, in the UK or anywhere else, is the difference between a body measurement and a garment measurement, and it is a bigger gap than most parents assume, by design rather than by accident. Referencing Winifred Aldrich, a standard reference for UK pattern cutting, younger children's blocks typically carry around 12 centimetres of ease at the chest and roughly half that, about 6 centimetres, at the waist, room to move and to layer, not a styling choice. Manufacturers commonly build in more than that again, 10 centimetres or beyond, specifically so that one size label can comfortably fit a wider spread of actual bodies, which is a commercial decision about how many sizes a business wants to cut and stock, not a comfort decision made for the child. A size chart that simply says 'this garment measures 60cm across the chest' leaves a parent to guess which of those reasons explains the gap. A size chart that says so plainly, expect roughly this many centimetres more than your child's own measurement, and here is why, turns a confusing number into something a parent can actually use, in a changing room or on a phone screen.
There is an old line about the definition of insanity being doing the same thing over and over and expecting a different result. It gets attributed to all sorts of people who probably never said it, so I will not put a name to it here, but the point stands regardless of who first made it. The industry's base blocks have been trusted for a long time without ever being properly questioned. Julia's data says that trust is overdue a second look, and having sat through that table reaching full agreement on the adult version of the problem, I am convinced the same is true for children's clothing too. So here is what this means for you: carrying both age and centimetres on a label costs nothing, two of the world's biggest retailers already prove it works, and explaining the honest gap between a body measurement and a garment measurement turns a source of confusion into a reason for a parent to trust your size chart, at home now and wherever you sell next.
FREQUENTLY ASKED QUESTIONS
What was the Tru-Size Roundtable, and who ran it?
The Tru-Size Roundtable was a session at the Real Circularity Summit (17 September 2026) run by Julia Reynolds, founder of Rey House and its technology arm Tru-Size, and previously the founder of Tesco's F&F clothing brand. Tru-Size uses generative AI and body scan data, more than 20,000 measurement points per avatar, to build size and grading models based on real body shapes rather than a single idealised sample size.
Why does age based sizing not work well for children's clothing?
Children of the same age can vary hugely in height and build, so a single age label, such as age five, assumes a narrow band of sizes that many children simply do not fit into. A measurement based approach, such as the European EN 13402 standard, which sizes by body measurement in centimetres, is already the de facto standard for children's clothing across most of Europe, with the UK a notable outlier still relying mainly on age.
What does poorly fitting product actually cost a retailer?
Beyond the immediate lost sale or return, an item returned twice or more can significantly damage the buying margin on that product through processing costs. Poor fit also encourages customers to order multiple sizes just in case, adding logistics cost and carbon footprint, and can leave a kept but ill fitting item unworn and eventually discarded, adding to landfill.
Do any major retailers already show both age and centimetres?
Yes. H&M sells the identical garment as an age-led size in the UK, with centimetres hidden behind a separate size guide, and as a centimetre-led size with age in brackets in Germany, at no extra operational cost. Zara shows age first for younger children on its UK site but sizes purely by height in centimetres from around age nine upward, treating age as a translation layer rather than the real size code.
Why is a garment measurement bigger than a child's actual body measurement?
By design, not by error. Referencing Winifred Aldrich's standard UK pattern-cutting guidance, younger children's blocks typically carry around 12cm of wearing ease at the chest and about 6cm at the waist, room to move and layer. Manufacturers often add considerably more again, 10cm or beyond, so that a single size label can fit a wider range of bodies, a commercial choice about how many sizes to cut and stock.
If you want to talk through how your own size charts and grading could better reflect your actual customers, whether that is adults or children, that is exactly the kind of conversation we have at The Nest. Come and talk to us.
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