And you can easily measure 16 rounds (it's double stacked) then use the measurement of the butt plate of the mag, and the tapered protrusion at the top. Add it up, and there it is.
Brian, I got this from a reliable friend.
.905” x 1.305” x 8.25”
that length measurement was from the tip of the follower, to the bottom of the base plate. The only measurement that should differ from a Glock 17/19/26 is the length