What gauge extension cord should I use for a lawn mower?

Use 14-gauge for a lawn mower. 16-gauge is too thin and can cause voltage drop, preventing startup or overheating the motor. 14-gauge works for most residential mowers up to 100 feet; for longer runs or heavy-duty mowers, step up to 12-gauge. Don’t risk a fire or a dead mower to save a few bucks.