As the insoles will be fitted inside your shoe, it’s most important that you match your shoe’s size rather than your foot measurement. You will be trimming the insole to match your shoe's original insole.
TIP: We find that the EU size is the most universally consistent measurement of shoe sizes.
If you're in between sizes (e.g. your shoe is a 43.5 between a Med and Large):
if you plan to wear them in everyday shoes (runners, boots etc)... size up
if you plan to wear them in cycling shoes, ice skates ski boots or any other shoe with a slim-fitting front - these types of shoes typically have a much tighter fit and a narrower toe box... size down.