US: 6.5 to Europe Size 44

US: 6.5: Features an inner diameter of 16.9 $\text{mm}$ (0.665 $\text{in}$), inner circumference of 53.1 $\text{mm}$ (2.09 $\text{in}$), and standard numerical or letter ring scales optimized for women’s sizing curves.

Europe Size 44: Features an inner diameter of 14.1 $\text{mm}$ (0.555 $\text{in}$), inner circumference of 44.2 $\text{mm}$ (1.74 $\text{in}$).