CN 42 is a common men's shoe label on Chinese shopping sites. The safest check is the foot-length value in centimeters.
Quick answer: CN 42 is about US men's 8.5, UK 8 and EU 42. The usual foot length is 26.5 cm / 10.4 in.
For sneakers, CN 42 can be fine for a 26.5 cm foot if the toe box is not narrow.
For pointed or narrow dress shoes, consider width and reviews before ordering.
US men's sizing differs from US women's sizing even when the CN number is the same.
Measure both feet and use the larger foot.
This page answers one specific size search intent. For the best fit, start with the linked main converter and use the centimeter measurements on the Chinese chart whenever they are available.
Marketplace labels are useful shortcuts, but brand charts, garment type, fabric stretch and body measurements can change the final fit. Treat the lookup as a nearest match, not a guaranteed size.
Chinese size labels are practical lookup shortcuts, not universal brand guarantees. A CN shoe label, clothing size, bra code or Taobao chart row can vary by seller, product category, last shape, fabric stretch and whether the chart shows body measurements or garment measurements.
When possible, use the centimeter value first: foot length for shoes, bust/waist/hip for clothing, under-bust and cup difference for bras, and the specific Taobao chart row for marketplace listings. Then use the converter result as the nearest US, UK or EU match.
For the broader explanation, read Chinese shoe size chart to US complete guide. For why these pages give estimates instead of promises, read Chinese shoe sizes and foot length.