My daughter's foot is 6 1/2 inches or 17 cm and she wears size 10 street shoes. Based on reviews I ordered her slippers 1 size up and received her size 11C and they fit perfectly! She has a narrow foot, but the "C" fits her perfectly and she still has room to grow. Very well made shoes and they should keep them.
Adorable Blowfish Malibu Play-t for Toddler and Little Girls
47 Review
Flexible Comfort: pediped Flex Isabella Mary Jane for Toddlers and Little Kids
47 Review
Felix Flora Toddler Flower Dress Shoes - Adorable and Comfy Flats
47 Review
Slip-Resistant Crib Shoes for Babies: Robeez Soft Soles for Girls and Unisex Toddlers, Ages 0-24 Months
53 Review