There are two common leash thicknesses, often referred to as competition leashes and regular leashes. Competition leashes are usually around 3/16ths of an inch thick while a regular leash will be closer to 5/16ths of an inch thick. For all you metric users out there, that’s roughly 4.7mm and 8mm, respectively. When deciding on thickness you should consider the length of your board, wave height, and your surfing experience and ability level.