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AI sizing study 2026: what AI assistants see in 1,383 clothing stores
For 80% of the 1,383 UK and US Shopify clothing stores we checked, the product we sampled reached AI shopping assistants with no size chart and no measurements. Only 4% carried a full size chart. When an assistant such as ChatGPT is asked which size to buy and has nothing to read, it still names a size.
By Sienna Stones · Published 2 November 2026 · Data collected 21–22 October 2026
Results
| What the sampled product carried | All stores (1,383) | UK (1,017) | US (366) |
|---|---|---|---|
| No size chart or measurements | 1,104 (80%) | 814 (80%) | 290 (79%) |
| Some measurements, not a full chart | 180 (13%) | 125 (12%) | 55 (15%) |
| A pointer to a size guide elsewhere, without its contents | 40 (3%) | 31 (3%) | 9 (2%) |
| A full size chart | 59 (4%) | 47 (5%) | 12 (3%) |
Percentages are rounded, so a column may not add to exactly 100.
Why the charts don't arrive
Most of these brands do publish sizing for shoppers. In our earlier size chart report of 829 Shopify fashion stores, 32% showed a text size chart on the product page and 27% a picture of one. But AI assistants don't read the page a shopper sees. On Shopify they receive products through Shopify Catalog, and charts drawn by a size-chart app, shown as images or kept on a separate size guide page don't travel with it. Our guide What is an AI size chart? explains the difference and how to fix it.
What assistants do with no chart
In a separate test on 2 October 2026, ChatGPT matched the brand's own chart for 14 of 15 products where the chart was readable. Where it wasn't, it named a size every time, and 13 of 14 letter-size answers were Medium. That test was small and non-random, run on one day with two mid-range shopper profiles, where Medium is often a reasonable answer.
Method
- Stores: 1,383 Shopify clothing stores selling to the UK (1,017) or the US (366), drawn from our own list of fashion brands.
- Sample: one clothing product per store.
- Source: the product as returned by Shopify Catalog, the product data Shopify shares with AI channels, looked up on 21 and 22 October 2026. We did not read the product page itself.
- Classification: whether the product data carried a full size chart (labelled measurements for each size), some measurements, only a pointer to a size guide, or nothing about size beyond the size names.
- Limits: one product per store, so a store can carry a chart on other products; one point in time; our own list of brands, not a random sample of all Shopify stores.
Data
Download the anonymised results: ai-sizing-study-2026.csv (1,383 rows: market and what the sampled product carried; store names removed). Free to reuse under CC BY 4.0 with a link to this page.
Cite as: Rendered Fits (2026). AI sizing study 2026: what AI assistants see in 1,383 clothing stores. https://www.renderedfits.com/ai-sizing-study-2026/
Check your own store
The free AI size chart checker runs the same lookup on your store's products and shows what comes through: size chart, fit advice and model size. No install, no sign-up.
About Rendered Fits. Rendered Fits is a Shopify app for fashion brands that recommends a size for supported products from the brand's own size chart, and can show shoppers an optional AI try-on preview. There is a Free plan, and Complete is $349 a month with a 14-day trial.
Related: what is an AI size chart? · Shopify size chart report 2026 · AI shopping agents statistics · AI size chart checker