There's a size chart at the top of this page, open it and find yours.

It converts between UK, EU and US sizing, so whichever you normally shop in you can match it across. Check it against a shoe that already fits you well rather than going from memory, sizing drifts a lot between brands.

If you're between two sizes, go for the bigger one. You can trim an insole down. You can't make one bigger.

To trim them: take the insole out of the shoe you're going to wear them in, lay it on top of the new one, and cut around it at the toe end with scissors. Take a little off at a time and keep trying it in the shoe as you go, it's easier to cut twice than to start again. Leave the heel and arch alone; that's the shaped part doing the work.

Still not sure? Email us your usual size and the shoes you'll be wearing them in, and we'll tell you which to order. And if you do get it wrong, the 30-day guarantee covers it.