How do I know what size strap bindings to get?

Check the specific manufacturer's size chart, as sizing ranges vary between brands. Match the binding size to your snowboard boot size (not your street shoe size). If you're between sizes, consider your boot's bulk — thick-soled boots may fit better in the larger size. The boot should sit fully within the baseplate with the heel firmly against the heel cup and straps reaching comfortably without maxing out the ladder.