Why one shoe number is not enough across brands
Two shoes carrying the same number may fit differently. Conversion helps read a label and compare a manufacturer’s chart; it does not turn foot shape or width into a fit guarantee.
A reference chart, not a universal law
Nike’s chart connects EU, UK, US men, US women and JP/CM. The source warns that the CM label is not measured foot length. Do not enter a foot measurement as a JP label and treat it as a direct fit test.
References: Nike
Children are a separate system
Children’s US sizes use C and Y labels and separate rows. Choose the child group first and retain the letter in 1Y or 8C: it carries meaning, not decoration.
References: Nike — Kids’ footwear size chart
A label can have multiple matches
In the adult reference, EU 42 maps to UK 7.5, US men 8.5, US women 10 and JP 26.5. These come from one row, not a guarantee across every brand.
UK 6 appears in two adult rows, mapping to EU 39 and EU 40. Showing only one hides information. Check another label such as EU or US to identify the row.
When changing brands, use that brand’s chart, measuring instructions and returns policy. Length, width and model shape influence fit; EU alone does not establish width.