First base mitts are measured differently. They're no bigger than any other glove. Just made with stiffenedfor digs . Wilson offers free shipping and returns if you want to check them out.or this one
We designed the 2820 based on the feedback of some of the best first baseman in the game. Built with an extra quarter-inch of length and crafted for better comfort over the course of the season, this first base mitt is ready to take your game to the next level.www.wilson.com
12.25" would seem to be a bit too small for fastpitch,, no? Like I said, never had to deal with 1B mitts before so I have no idea.