Size recommender

A size recommender does the matching between a shopper's body and a size chart, and answers with one size: "Your size: M". It sits in the size guide or next to the size selector. The good ones say why, say how sure they are, and refuse to push a size that doesn't exist.

Recommenders differ by what they ask for:

1. Measurements. The shopper types the measurements the chart lists, and the tool compares them with each size. It can explain itself line by line and works on a product launched today, but the shopper needs a tape.
2. Height, weight and age. Equations from body surveys estimate the measurements. No tape, but two people of the same height and weight can have quite different chests, so the honest answer is an estimate.
3. Quizzes and models trained on past orders. No tape either, but they need order history, and their answer is hard to check against the chart.

In Ruban Size

Find my size is the first kind, on every plan. It gives one size, a confidence (high, medium or low), one line per measurement ("Chest 92 cm: M, middle of the range"), the neighbor size when it is a real alternative, and a sentence when the shopper is between two sizes. It knows 20 product categories, adds ease to garment measurements and follows the chart's fit scale. Measurements stay on the shopper's device, never sent.

On the Fit plan it adds the second kind, with the ANSUR 1988 equations (Cheverud et al. 1990) and Bozeman et al. 2012 for the waist. The answer is shown as an estimate with the chances of each size ("M 55% · S 24% · L 19%"), and never for under 18s.

Tested on 40,000 simulated shoppers drawn from NHANES 2015 to 2018 and ANSUR II, Find my size gave the exact size 65.8% of the time and the size or the next one 94.5%, against 49.2% and 72.1% for a plain lookup in the chart. What a size recommender is compares the three kinds.