This is a medium sheath for medium utility knives. The length of the knife is up to you, depending on how much of the handle you want to be left sticking out. Just measure your knife starting at the tip, and once you hit the spot on the knife where the opening of the sheath will be (using the sheath depth measurement below), measure the circumference of the handle at that spot to make sure it will fit. The most important measurement is the blade width, because the sheath has a plastic liner so will only accommodate blades up to the maximum width listed below.
Sheath Length: 8.25 inches Sheath Depth: 7.5 inches Sheath Opening Width: 1.1 inches Max Handle Circumference: 3.5 inches Max Blade Width: 0.9 inches Belt Loop: 2 inches