Chinese baby clothes are usually labeled by height in centimeters. The height number is more useful than age because babies grow at different speeds.
Quick answer: Chinese baby size 66 is often around US 3-6 months, 73 is around 6-9 months, 80 is around 12 months and 90 is around 18-24 months.
A listing marked 80 is usually designed for a baby around 75-85 cm tall, not exactly every 12-month-old baby.
Check garment length, chest and sleeve length when buying coats or sleepwear.
Baby clothing varies by brand, diaper room and garment type.
Use child height in centimeters as the first check, then compare the seller chart.
This page answers one specific search intent. For a full table, reverse conversion, nearby sizes or live currency and calendar inputs, use the linked main converter.
When a Chinese listing includes both a label and a metric value, use the metric value first. Labels are useful shortcuts, but centimeters, kilograms and square meters are easier to verify.