Jumper cable gauge refers to the thickness of the jumper cable’s wiring. A standard set of jumper cables has a gauge rating of six. The smaller the gauge rating, the thicker the cables are. The thicker the cables are, the more effective they’ll be. Nevertheless, a set of jumper cables with a gauge rating of eight should provide enough power to jump start most vehicles. For larger vehicles with larger batteries, it may be necessary to use a set of jumper cables with a gauge rating of six, or even four or two. The lower the gauge rating, the more expensive the cables tend to be.
For more info, see How to Jump Start a Car Using Battery Jumper Cables