What wire size do I need for 20 amps?

For a 20-amp circuit, use 12 AWG copper wire or 10 AWG aluminum wire. This is per NEC Table 310.16 at 75°C insulation temperature. Common uses: kitchen, bathroom, and garage outlets.

What breaker do I need for 20 amps?

A 20-amp circuit uses a 20A single-pole circuit breaker. The breaker protects the 12 AWG copper (or 10 AWG aluminum) wire from overload. Double-pole breakers are used for 240V circuits and occupy two slots in the panel.

Can I use 14 AWG wire on a 20-amp circuit?

No — NEC prohibits using 14 AWG wire on a 20-amp breaker. 14 AWG is rated for 15A maximum. Always use 12 AWG copper (or 10 AWG aluminum) for any 20-amp circuit.

What requires a dedicated 20-amp circuit?

NEC requires dedicated 20A circuits for kitchen countertop outlets (at least two), bathroom receptacles, garage outlets, outdoor outlets, refrigerators, dishwashers, and microwave ovens. Each of these needs its own 12 AWG wire and 20A breaker.

What Wire Size for 20 Amps?

Copper Wire

12 AWG

2.0525 mm · 3.3088 mm²

Aluminum Wire

10 AWG

2.5882 mm · 5.2612 mm²

Breaker: 20A · Based on NEC Table 310.16 (75°C insulation)

Common Uses for 20A Circuits

Kitchen, bathroom, garage circuits

12 AWG Copper — Key Specs

Diameter	2.0525 mm (0.080808")
Area	3.3088 mm²
Resistance at 20°C	5.2104 Ω/km
Weight	29.647 kg/km
Ampacity (75°C)	25 A

Important: For long wire runs, you may need to upsize the wire to compensate for voltage drop. NEC recommends keeping voltage drop under 3% for branch circuits. Use our voltage drop calculator to check.

NEC 240.4(D) — why 12 AWG and not something smaller

NEC Table 310.16 rates 12 AWG copper at 25 A at 75°C, which looks like more headroom than a 20A circuit needs. It is not usable headroom. NEC 240.4(D), the small-conductor rule, caps the overcurrent device on 12 AWG copper at 20 A regardless of what the ampacity table says. The same applies to aluminum: 10 AWG aluminum shows 30 A in Table 310.16 but is capped at 25 A by 240.4(D).

This is why 12 AWG is the answer for a 20A circuit and why the next size down is not: the smaller conductor’s own 240.4(D) cap falls below 20 A. Any calculator that reads Table 310.16 without applying 240.4(D) will hand you an undersized, code-violating conductor.

The rule covers 18 through 10 AWG copper and 12 through 10 AWG aluminum. NEC 240.4(E) and 240.4(G) carve out narrow exceptions — tap conductors, motor circuits, air-conditioning equipment, and welders are sized under their own articles instead. See the full table on the wire size calculator.

Voltage Drop by Distance — 12 AWG Copper at 20A

One-way run	Drop	% of 120V	Verdict
25 ft	1.59 V	1.3%	Within the 3% branch-circuit target
50 ft	3.18 V	2.6%	Within the 3% branch-circuit target
75 ft	4.76 V	4.0%	Over 3% — upsize one gauge
100 ft	6.35 V	5.3%	Over 5% — upsize two or more gauges
150 ft	9.53 V	7.9%	Over 5% — upsize two or more gauges
200 ft	12.70 V	10.6%	Over 5% — upsize two or more gauges

Single-phase, 120V, full 20A load, 1.5881 Ω/1000 ft DC resistance (NEC Chapter 9, Table 8) at 75°C terminations. NEC 210.19(A) Informational Note recommends keeping branch-circuit drop at or below 3%, and 5% total across feeder plus branch circuit. Voltage drop is a performance recommendation, not a code requirement — but exceeding it causes dim lights, slow motor starts, and wasted energy.