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How many amps can 12 AWG wire carry?

25 A — copper at 75 °C, NEC Table 310.16.

12 AWG copper carries 25 A at 75 °C, 20 A at 60 °C and 30 A at 90 °C under NEC Table 310.16, before derating. NEC 240.4(D) then caps the breaker at 20 A, so 20 A is the usable answer. Aluminum at the same size is 20 A at 75 °C.

Safety first. These figures are an educational reference before derating, not a code substitute. Verify against the current NEC and have circuits reviewed by a licensed electrician.

12 AWG ampacity — copper vs aluminum

12 AWG ampacity by conductor material and insulation temperature rating.
Material 60 °C 75 °C 90 °C Breaker cap
Copper 20 A 25 A 30 A 20 A
Aluminum 15 A 20 A 25 A 15 A

Values are amps at a 30 °C ambient, before derating for temperature or conductor bundling. Most installations must use the 75 °C column regardless of the wire's own rating, because terminals and breakers are rated 75 °C (NEC 110.14(C)).

How far can you run 12 AWG at 20 A?

Ampacity answers whether a conductor will overheat. It says nothing about whether the voltage still arrives at the far end. Past roughly fifty feet, voltage drop is usually what really sets the wire size. These are the longest one-way runs that keep drop within the 3% recommended by the NEC 210.19(A) informational note, for 12 AWG copper carrying 20 A.

Maximum one-way run length for 12 AWG copper at 20 A by system voltage.
System Typical use Max run at 3% Drop at 100 ft
120 V standard receptacle and lighting circuits 57 ft 6.35 V
240 V ranges, dryers, EV chargers, feeders 113 ft 6.35 V
12 V DC automotive, marine, solar and battery runs 6 ft 6.35 V

Single-phase, one-way distance, copper at 20 °C. Aluminum reaches its limit at roughly 60% of these distances for the same size. The 3% figure is a recommendation in an informational note, not a code requirement.

12 AWG wire size — diameter, area and resistance

Diameter

0.0808 in · 2.053 mm

Cross-section

3.309 mm² · 6,530 cmil

Nearest metric size

4 mm² (rounds up)

Copper resistance

1.5882 Ω per 1000 ft @ 20 °C

Aluminum resistance

2.6523 Ω per 1000 ft

Area

6.53 kcmil

Diameter is computed from the ASTM B258 definition d = 0.005 × 92^((36 − n)/39), not read from a rounded table. Resistance uses the annealed-copper constant 10.371 Ω·cmil/ft at 20 °C.

What 12 AWG wire is used for

The 12 gauge mistake worth knowing

12 AWG copper is 25 A at 75 °C, yet it is universally a 20 A wire — 240.4(D) caps the breaker at 20 A. The gap between the ampacity table and the breaker cap is why “12 gauge = 20 amps” is right even though the chart says 25.