What gauge extension cord should I use for a circular saw on a 50-foot run?

Get the 12-gauge. A 50-foot run with 14-gauge drops voltage 5–7% under the saw’s load, causing bogging, overheating, and breaker trips. The 12-gauge keeps voltage drop under 3% and delivers full power. You can use 14-gauge only for short runs (25 feet or less) with light cuts, but for 50 feet, don’t cheap out.