CN 39 sits near the overlap between larger women's shoes and smaller men's shoes, so the US label depends on gender.
Quick answer: CN 39 is about US women's 8.5 or US men's 6.5. It usually means a 24.5 cm / 9.6 in foot length.
If the shoe is listed as women's CN 39, treat it as roughly US women's 8.5.
If the shoe is listed as men's CN 39, treat it as roughly US men's 6.5.
Always check whether the product is using a men's or women's size chart.
CN labels can be rounded from centimeter-based sizing.
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.