How many amps will 20 gauge wire carry?

Twenty gauge wire safely carries about 3 to 5 amps in typical low-voltage use, with chassis-wiring charts allowing more only for short, open-air runs. It is signal and electronics wire, not power wire.

You will meet it in thermostat cable, LED strips, automotive accessories, and speaker runs. It has no place on 120V branch circuits; the NEC's ampacity tables for building wire start at larger sizes for good reason.

At 12 volts the real constraint is usually voltage drop, not heat: 5 amps through 20 feet of 20 gauge loses enough voltage to dim LEDs visibly.

When a 12V accessory feels weak, the cure is almost always two sizes up, not more amps.

The 20 AWG amperage calculator shows safe current and drop for any run length.