It depends on the boot some (Seth, First Chair, Konflict) are 98mm, others (Classic, High Five, Hot Dogger, Booter) are "wide last" which is 100mm. However, it's hard to be exact because most of the last is in the liner and when it's heat molded it changes to your foot slightly, so for someone with the Seth it might be 98mm but someone else might have a 99mm last with the Seth - it depends on the molding.