The standard measurement for the width of an electrical wire is AWG, or American Wire Gauge, and the various widths of jumper cables, otherwise known as jumper cable gauges, are measured in this way. In the AWG measurement system, the largest measurement is a zero and the smallest measurement is a 40, so a zero gauge wire is the thickest at half an inch in diameter, while a 40 gauge wire is the thinnest at .001 inches in diameter. This odd system of measurement comes from the way that wire was produced in 13th century Europe. Wire was made at a desired length by being pulled through a series of smaller and smaller metal holes, each of which was one gauge higher and one increment thinner. Each hole would make the wire thinner by scraping a thin layer of copper from the wire.
The thickness of jumper cables is measured in the same way as any other wire or cable. Since the purpose of a jumper cable is to transmit enough power from one battery to another to start a car, the best jumper cables will be the ones that are capable of transmitting the most energy. Thicker cables can transmit more electrical current than thin ones.
Since thick heavy duty jumper cables are best at transmitting current from one battery to another, the best jumper cable to buy would be a low gauge cable. You may not need the absolute thickest jumper cables available in order to start your car; 0 gauge cables are used on semi trucks, but it is still a good idea to buy the thickest cables you can afford. This will reduce the chance that you won’t be able to transmit enough power to get the boost your car needs.