How far can you run a 12/2 wire on a 20 amp circuit?

Twelve-two on a 20 amp circuit runs about 50 feet at a full 20 amp load before drop passes the recommended 3 percent, and roughly 100 feet at a 10 amp load. The code sets no hard length limit; the volts do.

Real receptacle circuits rarely see sustained full load, which is why 70 or 80 foot bedroom runs on 12/2 work fine in practice.

For a known steady load at distance, a detached shed compressor for instance, size by the actual amps: at 16 continuous amps, 12 gauge gives out near 60 feet and 10 gauge takes over.

Rule of thumb worth keeping: one size up per additional 100 feet.

The 20 amp length calculator gives the exact cutover distance for your load.