US: 5 to Europe Size 40

US: 5: Features a foot length of 21.9 $\text{cm}$ (8.6 $\text{in}$), ball width of 8.2 $\text{cm}$ (3.2 $\text{in}$), heel height of 5 $\text{cm}$ (2 $\text{in}$), and Medium Arch support optimized for women’s footwear.

Europe Size 40: Features a foot length of 25.4 $\text{cm}$ (10 $\text{in}$), ball width of 9.4 $\text{cm}$ (3.7 $\text{in}$), and heel height of 9 $\text{cm}$ (3.54 $\text{in}$), and Universal Arch support optimized for women’s footwear.