it is a single stack, 8+1 of 45acp. i got to put about 100 rounds through her yesterday. although i did a lot of research before buying this gun i was still pretty surprised with how well it performed. the accuracy was as good as my hand is steady and i had no problem emptying whole clips into center mass of a life sized dummy 25 yards away. even though the gun is pretty light @ 29oz it's very well balanced with little recoil. i like it a lot more than the xd, m&p, glocks and even the sigs or hks i've shot. it's the best feeling polymer frame auto i've fired to date.