^^^ Either that or contact Burton. They are a large company so I'm not sure how quick they are to respond. Measuring the footprint of the boot might be helpful if you contact them.
When I bought my Ride bindings my boots were on the cusp of L vs. XL. They told me if I had a larger footprint 10.5 I might want the XL, unless I like to be really tight in the binding. Since I was buying a Ride boot in size 10 I knew I wouldn't really have a problem. Bindings are pretty flexible for sizing. I expanded mine to be as big as it could get and my original boots fit fine.