You need to look at the specs for that model of MacBook Air you are planning on purchasing. It will tell you the maximum storage ssd it will take, which on most MacBook airs is 220Gb. Also make sure if you get a deferent brand of ssd that it fits in the area for the ssd and it doesn't go over the screw hole at the end. Most likely it's a better idea to get a 120 to 220gb ssd from apple to make sure it's compatible. But if you find a ssd from another brand that's cheaper again make sure it fits in the rectangle and doesn't go over the screw hole.