US: 6 to Europe Size 40

US: 6: Features a foot length of 22.9 $\text{cm}$ (9 $\text{in}$), ball width of 8.5 $\text{cm}$ (3.3 $\text{in}$), heel height of 6 $\text{cm}$ (2.4 $\text{in}$), 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.