How to Identify Tire Chain Size by Number of Linksby Pat Smith
Tire chains, also known as snow chains, go on winter tires for added traction in snow and ice. They are invaluable in any location with heavy snowfall, such as Alaska, the upper Midwest, and the mountains of the United States. They are only effective if they fit the tires correctly. They should also not be used on dry terrain in normal weather--they're only for winter use. Tire chain links come in a few sizes of material, so you can easily calculate the length of the chain based on the number of links.
Locate the material size of the links, which would be part of any original packaging that came with the tire chain. If you no longer have it, measure one of the links. Since part of the link length is "lost" in connecting to the next link, measure from the bottom of the last link up to the bottom of the next link. The 9/0 links are 1.2625 inches, while 8/0 are 1.2375 inches, and 7/0 are 1.0909 inches.
Count the total number of links twice. If your numbers differ, recount.
Multiply the number of links by the link size that matches up with the material size you deduced for your tire chain. For example, if you have 7/0 links, and you counted 12 links, multiply 12 x 1.0909 for 13.0908 inches, or just over 13 inches.