It's really pretty simple. 1 set of ski/snowboard equipment counts as 1 checked item. 1 set of equipment can be two bags - 1 for skis/bindings/poles or snowboard/bindings and another for boots. There is no extra charge for oversize bags containing ski/snowboard equipment so no linear measurement limit. You'll either pay the fee for 1 checked bag for ski/snowboard equipment or not, depending on the normal fee exceptions.

Jim