If you need the direct answer for standard residential copper wiring: 14 AWG is rated for 15 amps, 12 AWG is rated for 20 amps, and 10 AWG is rated for 30 amps. These baseline values are fixed by the NEC 60°C ampacity column, which governs standard NM-B (Romex) cable and the termination limits of most residential breakers and receptacles.
However, ampacity is a thermal limit, not a simple Ohm's law conversion. The formula that actually dictates your wire's safe current capacity under real-world conditions is the NEC derating formula: Adjusted Ampacity = Base Ampacity × Temperature Correction Factor × Bundling Correction Factor. For example, if you pull 12 AWG THHN (base 30A at 90°C) through a hot 40°C attic (0.87 temp correction) alongside three other current-carrying conductors (0.80 bundling correction), your math is: 30A × 0.87 × 0.80 = 20.88 usable amps. Because 20.88A is above the standard 20A breaker threshold, the wire remains safe, but you cannot upsize the breaker.
The Core AWG to Amps Chart (NEC Table 310.16)
The most common mistake DIYers make is using the 90°C column to size their breakers. Unless your lugs and breakers are explicitly rated for 90°C (almost none in residential spaces are), you must use the 60°C column for NM-B cable and circuits under 100A, or the 75°C column for THHN/THWN in conduit. The table below outlines the standard copper limits based on the National Electrical Code (NEC).
| AWG Size | 60°C Column (NM-B) | 75°C Column (THHN in Conduit) | 90°C Column (Derating Only) | Max Standard Breaker |
|---|---|---|---|---|
| 14 AWG | 15A | 20A | 25A | 15A (NEC 240.4(D)) |
| 12 AWG | 20A | 25A | 30A | 20A (NEC 240.4(D)) |
| 10 AWG | 30A | 35A | 40A | 30A (NEC 240.4(D)) |
| 8 AWG | 40A | 50A | 55A | 40A / 50A |
| 6 AWG | 55A | 65A | 75A | 60A |
| 4 AWG | 70A | 85A | 95A | 70A / 80A |
Note: NEC 240.4(D) strictly limits small conductors (14, 12, and 10 AWG) to their 60°C equivalents for overcurrent protection, regardless of the insulation's higher thermal rating.
Why Voltage, Phase, and Power Factor Don't Change Ampacity
A frequent point of confusion is assuming that an AWG to amps chart shifts based on system voltage. It does not. A 10 AWG copper wire will physically overheat and melt its insulation at the exact same current (roughly 35A continuous in free air) whether it is carrying 12V DC, 120V AC single-phase, or 480V 3-phase.
What actually shifts is the load calculation. Voltage, phase, and power factor (PF) dictate how many Watts your load draws, which you then convert to Amps to select your AWG.
- 120V vs 230V: A 2400W heater draws 20A at 120V (requiring 12 AWG), but only 10A at 240V (requiring 14 AWG). The wire's capacity didn't change; the load's current demand did.
- 3-Phase Shifts: In a 3-phase system, current is calculated as
I = P / (V × √3 × PF). The √3 (1.732) reduces the current per leg compared to single-phase, allowing smaller AWG wire for the same total wattage. - When the Conversion is Meaningless: If you are sizing wire for an industrial AC motor and the Power Factor (PF) is unknown, converting the motor's kW rating to Amps is a guess. A motor with a poor PF (e.g., 0.6) will draw significantly more current than a motor with a high PF (e.g., 0.95) for the exact same mechanical output. Always use the motor nameplate Full Load Amps (FLA) rather than calculating from kW when PF is unverified.
Neighboring Values: 10, 12, and 14 AWG Deep Dive
Because 90% of residential branch circuits rely on these three sizes, here is a focused look at their physical properties and strict NEC limitations.
| AWG | Diameter (Inches) | Resistance (Ω/1000ft) | Common Use Case | Max Breaker |
|---|---|---|---|---|
| 10 AWG | 0.1019" | 0.9989 Ω | Electric dryers, 30A RV outlets, water heaters | 30A |
| 12 AWG | 0.0808" | 1.588 Ω | Kitchen small appliances, bathroom GFCI, outdoor receptacles | 20A |
| 14 AWG | 0.0641" | 2.525 Ω | Bedroom lighting, living room general receptacles | 15A |
FAQ: Common AWG to Amps Sizing Mistakes
Can I use the 90°C column to get more amps out of my THHN wire?
No. According to OSHA and NEC guidelines, the 90°C column is strictly used as your starting point for derating calculations (adjusting for ambient heat or bundling). Your final calculated ampacity must still be capped at the 60°C or 75°C column, because the brass and steel lugs inside standard residential breakers and receptacles are not rated to dissipate heat beyond 75°C.
Does the AWG to amps chart change if I use Aluminum wire?
Yes, significantly. Aluminum has higher electrical resistance and a different thermal expansion rate than copper. For example, to achieve the same 30A rating that 10 AWG copper provides, you must step up to 8 AWG aluminum. Always check the "Aluminum" columns in NEC Table 310.16, and ensure your terminations are rated for aluminum (marked AL/CU) and treated with an anti-oxidant compound like Noalox to prevent high-resistance arcing over time.
What happens if I put a 20A breaker on 14 AWG wire?
This is a severe fire hazard. 14 AWG wire is physically limited to 15A. If a fault or overload pulls 18A through the circuit, the 14 AWG wire will begin to overheat and melt its insulation long before the 20A breaker's thermal trip mechanism engages. NEC 240.4(D) explicitly forbids this mismatch. Always match the breaker to the wire's lowest rated column.
