What gauge wire do I need for 20 amps?

For 20A circuits, 12 AWG copper at 75°C terminations is a common starting point (rated 25A). Always verify with NEC Table 310.16 and check derating for conduit fill and ambient temperature.

Do I need to account for voltage drop?

Yes, on runs over 50 feet voltage drop often requires a larger wire than ampacity alone. Use a voltage drop calculator to check.

What Gauge Wire for 20 Amps?

Wire size depends on more than amps: insulation type, ambient temp, how many wires share the conduit, and how it is installed. The info below is a starting point only. We are not liable for decisions you make or how you use this in the real world. Verify with NEC Table 310.16 and a licensed electrician for any permanent installation. Full disclaimer

Quick Reference: 20A Circuit

Wire Gauge (Copper)	Ampacity at 75°C	Notes
12 AWG	25A	12 AWG copper is rated 25A at 75°C. Required for 20A circuits per NEC.

Values from NEC Table 310.16, copper, 75°C, up to 3 conductors in raceway, 30°C ambient. Derating applies for higher temperatures or more conductors in conduit.

Why "What Wire for 20 Amps?" Has More Than One Answer

Insulation temperature rating: 60°C, 75°C, and 90°C insulation have different ampacity columns in NEC Table 310.16. Most devices terminate at 75°C, so that column is typically the right one.
Ambient temperature: Higher ambient means the wire cannot shed heat as well. NEC Table 310.15(B) has correction factors.
Conduit fill and bundling: More than 3 current-carrying conductors in a raceway requires derating per NEC Table 310.15(C)(1).
Copper vs. aluminum: Aluminum has higher resistance, so you need a larger gauge to match copper ampacity.
Voltage drop: On runs longer than 50 to 100 feet, voltage drop often drives wire sizing above what ampacity alone would require.

Ampacity Table Reference (Copper, 75°C, Up to 3 Conductors)

Gauge	Ampacity	Gauge	Ampacity
14 AWG	20A	1/0 AWG	150A
12 AWG	25A	2/0 AWG	175A
10 AWG	35A	3/0 AWG	200A
8 AWG	50A	4/0 AWG	230A
6 AWG	65A	250 kcmil	255A
4 AWG	85A	300 kcmil	285A
3 AWG	100A	350 kcmil	310A
2 AWG	115A	400 kcmil	335A
1 AWG	130A	500 kcmil	380A

Approximate values from NEC Table 310.16. Verify with the current edition of the NEC.

Calculate Your Wire Size

Enter your load, voltage, run length, and the calculator finds the minimum gauge that meets both ampacity and voltage drop limits:

Open Wire Size Calculator →Single-Phase Voltage Drop →Conduit Fill Calculator →

Common Questions

Where do I find official wire ampacity tables?

NEC Table 310.16 covers conductors in conduit or cable with up to 3 current-carrying conductors. Other tables apply for direct burial, free air, and other conditions. Your electrical inspector or AHJ may require a different table depending on the installation type.

Can I just use a wire gauge chart I found online?

Many online charts skip correction factors for temperature and conduit fill. Cross-check with the actual NEC table and get a licensed electrician to review any permanent installation.

What is the difference between ampacity and voltage drop sizing?

Ampacity is about not overheating the wire. Voltage drop is about the load still seeing enough voltage. On long runs you often need bigger wire to control drop than you would for ampacity alone.

What if I need to put multiple wires in a conduit?

You will need to derate the ampacity. NEC Table 310.15(C)(1) lists adjustment factors: for 4-6 conductors, multiply by 0.8; for 7-9, by 0.7; and so on. Use our conduit fill calculator to check whether the conduit is large enough first.