How Shoppers Find a Clothing Size from Height and Weight
Most people will not tape their chest in a bedroom at 22:00. They know their height and weight. The useful product is a size from those two numbers - not a lecture about measuring.
That is Estimate my size in AI Frame (Starter and above). It is not a selfie. It is not ChatGPT. It is declared height, weight, and gender (age optional) → estimated chest, waist, and hip in cm → the published Size Chart on that product → Your size.
Why height and weight at all
Fit is garment minus body. Ease. A chart of centimetres is the right language. The bottleneck is getting the body numbers.
Certainty falls as you add inputs. Ask for seven measurements, you get silence and a guess. Ask for height and weight, you get an answer most people can give - including a gifter who is not the wearer (holiday).
Zalando has said items with size advice had 10% fewer size-related returns than similar items without it. Advice that requires a tape still fails the people who will not use a tape. Height and weight is how you put advice in front of them.
What AI Frame actually does
- Shopper taps Estimate my size (or Help us find your size when empty).
- Enters height, weight, gender. Age optional.
- We estimate chest, waist, and hip with linear regressions fitted on the public ANSUR II dataset (U.S. Army anthropometry, on the order of 6,000 people).
- Those centimetres are read against your Size Chart for that product — body or garment, fit intent, stretch 0–20% if you set them.
- The card can show Your size. The picker can follow.
RMSE on those estimates is about 2.5–4.8 cm depending on the measure. Size bins on clothing charts are often 4–6 cm wide. That is good enough to pick a row, not good enough to claim a millimetre-perfect body scan. We say so.
What we never do
We never infer body attributes from the uploaded try-on photo. Height, weight, age, chest - not from pixels. That is a GDPR and EU AI Act line. The photo is for will it suit me. The numbers are for will it fit me. Mixing them is how you get a creepy product and a wrong size.
ChatGPT’s Try On (1 October 2026) is explicit: the image does not guarantee fit or size. Neither does ours. ChatGPT added try-on. Shoppers still don’t know their size.
We do not estimate foot length from height and weight. Shoes need a foot-length Size Chart.
We do not pick a bra cup. Chest circumference is not a cup. Swimwear still needs bust / underbust on the chart.
We do not replace the Size Chart. If the table is wrong, the size is wrong. Body vs garment has to be set. A garment measured flat is not a body.
How shoppers should think about the numbers
Height in cm (or feet/inches if they toggle - we still compute in cm). Weight in kg. Gender because the ANSUR II fits are sex-specific; that is the dataset, not a branding exercise. Age helps a little; it is optional so a gifter is not blocked.
If they know their chest in cm, a good chart still lets them skip the estimator and read the row. The estimator is for everyone else.
If the garment is oversized on purpose, fit intent on the chart should say so, or a correct body will still get a size that looks “too big” in the mirror. Stretch on jersey vs rigid denim is the other lever (0–20%). Same body, same labelled size, different correct SKU.
Merchant setup
Size Recommender is Starter $19.99 and above. Free plan is Size Chart and Try On only.
You still need a published, assigned Size Chart. Estimate my size has nothing to read otherwise. Five steps, no code.
On OS 2.0, Add Sizing assist in Get started (or the Sizing assist block). Vintage themes keep the embed.
Show Your size near the variant picker when you have it. That is the persistent badge. The architectural point: sizing cannot live only inside try-on. Most people never start a try-on. Height and weight is how those people still get a size.
Honesty about ANSUR II
ANSUR II is military-age adults, U.S., with the selection that implies. It is public, documented, and better than a guess. It is not your Belgian customer in her sixties. RMSE 2.5–4.8 cm is why we do not sell this as a body scan. We sell it as “closer than ordering two sizes.”
Kids, pregnancy, limb difference: the chart and a human, not the regression. Do not put Estimate my size on a product where the chart is shoes or cup-only.
Why this belongs next to Virtual Try-On
Look and fit are independent. A render on their photo can be perfect while the waist is 5 cm short. Height and weight does not make the jumper look better. It names a size so they add one to cart.
Shopify: shoppers who can visualize products convert up to 94% better (3D Ecommerce + changelog, 11 May 2022) - visualization category, not us. Put Try On on the image. Put this on the size. Do not make one wait for the other.
Install AI Frame and turn on Size Recommender on Starter. The Size Chart on Free is the table the estimator will read once you upgrade.
