Nike vs ASICS Shoe Size - Which Runs Smaller?

Nike runs about half a US size small compared to ASICS. If you wear Nike in US 9, start by checking ASICS in US 8.5. Both brands use the same foot-length measurement; the difference is in the last shape, not the conversion formula.

Nike to ASICS size chart

Starting ASICS size to check when you wear Nike in each US men size.
US Men (Nike) Nike -> ASICS Foot length
7 6.5 246mm
8 7.5 254mm
9 8.5 262mm
10 9.5 271mm
11 10.5 279mm

Fit verdict

  • Nike: Runs small (55% of buyers)
  • ASICS: True to size (75% of buyers)

Why the sizes differ

Nike runs about half a US size small compared to ASICS, with roughly 4mm between the matched fit records.

Nike foot length is measured in millimetres, then mapped to US size. The ASICS starting size shifts by about half a US size because of each brand fit bias, not a different conversion formula.