He advises sticking to this chart when choosing an extension cord gauge: Extension Cord Gauge What You Can Safely Plug In ; 12- to 10-gauge: Space heaters, power tools, ...

A cord measuring 14 AWG is the thinnest we recommend—and at lengths of only 25 feet or shorter—and the much thicker 10 AWG is likely the thickest gauge you’ll find in an extension cord.