To determine which Mirrix Loom you have, simply measure the top beam of your loom from left to right. That number in inches is your loom size.
The Saffron Pocket Loom: This is the only exception to this rule. It is 5" wide and has only one vertical beam.
The 5" Mini Mirrix: 5" Wide
The 8" Lani Loom: 8" Wide
The 12" Little Guy Loom: 12" Wide
The Easy Warp Sam Loom (which has been discontinued) is also 12" wide and is basically a Little Guy Loom frame. You can use any Little Guy accessory on this loom.
There is a Tall Edition 12" Little Guy Loom that is taller than the regular 12" Loom. You can find its measurements here.
The 16" Big Sister Loom: 16" Wide
There is a Tall Edition 16" Big Sister Loom that is taller than the regular 16" Loom. You can find its measurements here.
The 22" Zach Loom: 22" Wide
The 28" McKinley Loom: 28" Wide
The 32" Joni Loom: 32" Wide
The 38" Zeus Loom: 38" Wide
The 48" Lily Loom: 48" Wide