If you don't know which Tire Chain will fit on your Tire or don't know your Tire size then you need to measure your Tire first.
Tire Chain size is generated by Tire Height X Tire Width X Rim Diameter
Example: Tire Chain for Tire Size 25x8x12, 22x9x12, 23X6.5x12
This means this Tire chain will fit for these 25x8x12, 22x9x12 and 23X6.5x12 size Tires.
There is another way to describe tire size like 4.1/3.5x4, 3.4/3x5
Example: Tire Chain for Tire Size 4.1/3.5x4
Here the first "4.1" is the Tire Width, the second "3.5" is the Tire Height of the sidewall (not the total height), and the third "4" is the rim diameter. So a 4.1/3.5-4 tire is 4.1 inch wide, 3.5 inch tall on the sidewall, and fits a 4 inch rim