We successfully supply many boots online. There will always be an element of uncertainty about sizing but we have found the following advice works for approximately 90% of our online customers.
Medium/wide feet - go up 1/2 size on your SHOE size (to allow for thicker socks with boots). Narrow feet - stick with your SHOE size.
If you have a history of boot or shoe fitting problems it's best not to order online. You'll need to visit the factory for a fitting assessment. Contact the factory in advance - for an appointment with one of our senior boot fitters.