AWG to Amps Conversion Chart: Sizing Wire for 120V, 240V, and 3-Phase

When converting AWG to amps for standard residential copper wire, the direct baseline answers are: 14 AWG = 15 Amps, 12 AWG = 20 Amps, and 10 AWG = 30 Amps. These values assume copper conductors with 60°C rated insulation (like standard NM-B/Romex) used in branch circuits under the small conductor rules of NEC 240.4(D). There is no single mathematical formula to convert American Wire Gauge (AWG) directly to amperage because AWG measures physical cross-sectional area, while ampacity measures thermal heat dissipation limits based on insulation type and installation environment.

The "Formula" for AWG to Amps (And Why It's Actually a Thermal Limit)

Because ampacity is a thermal threshold rather than a fixed geometric ratio, electrical engineers and electricians do not use a simple algebraic conversion. Instead, the "formula" used to determine the real-world ampacity of a specific AWG wire is the NEC Derating Calculation. This adjusts the base table value for environmental heat and conductor bundling.

The formula is:
I_adjusted = I_base × C_temp × C_bundle

Worked Example with Substituted Values:
Suppose you are running 10 AWG THHN (which has a base ampacity of 40A in the 90°C column of NEC Table 310.16) through an attic that reaches 113°F (45°C), and you are pulling 4 current-carrying conductors in the same conduit.

• I_base: 40A (90°C column for 10 AWG THHN)
• C_temp: 0.87 (Temperature correction factor for 45°C ambient)
• C_bundle: 0.80 (Adjustment factor for 4-6 conductors in a raceway)

Calculation: 40A × 0.87 × 0.80 = 27.84 Amps.
Because 27.84A is less than the 30A limit of the 60°C column, you cannot protect this wire with a 30A breaker under these specific attic conditions. You must step up to 8 AWG to maintain a safe 30A circuit.

How 120V, 240V, and 3-Phase Shift the "Conversion"

A critical misconception in electrical sizing is that voltage or phase changes a wire's ampacity. The thermal ampacity (AWG to Amps) does not change with voltage or phase. A 10 AWG copper wire will overheat at the exact same amperage whether it is carrying 12V DC, 120V single-phase AC, or 480V 3-phase AC. The physical melting point and insulation degradation threshold are purely a function of current (I²R heating).

What does shift when you change from 120V to 240V or 3-phase is Voltage Drop and Power Delivery (Watts):

• 120V Single-Phase: High current for a given wattage. Voltage drop is calculated using the standard single-phase formula: VD = (2 × K × I × L) / CM. You will hit the 3% voltage drop limit much faster on long runs.
• 240V Single-Phase: Halves the current for the same wattage (e.g., a 4800W water heater draws 40A at 120V, but only 20A at 240V). This allows you to use smaller AWG wire for the same power load.
• 3-Phase (208V/480V): Uses the √3 multiplier in voltage drop calculations. 3-phase systems deliver more power with less current per conductor, meaning you can use a smaller AWG wire for heavy industrial loads compared to single-phase.

Neighboring Wire Sizes and Ampacity Reference (±20% Range)

The table below focuses on the most common DIY branch circuit sizes, centered around the 10 AWG / 30 Amp baseline, showing how the physical size shifts the thermal limits. All values assume copper conductors.

Note: Data sourced from NFPA 70 (NEC) Table 310.16 and 240.4(D). Always verify with your local Authority Having Jurisdiction (AHJ), as local amendments may restrict 14 AWG use entirely.

Frequently Asked Questions

How many amps can 12 AWG wire handle at 240 volts?

12 AWG copper wire is still limited to 20 Amps at 240 volts. Voltage does not change the thermal ampacity of the wire. What changes is the total power (Watts) the wire can deliver. At 120V, a 20A circuit delivers 2,400 Watts. At 240V, that same 12 AWG wire and 20A breaker can safely deliver 4,800 Watts, which is why 240V is used for heavy appliances like dryers and EV chargers.

Does power factor (PF) change the AWG to amps conversion?

Power factor does not change the physical ampacity limit of the wire, but it drastically changes the actual current the wire must carry. In AC circuits with inductive loads (like motors or transformers), a low power factor (e.g., 0.70) means the wire must carry significantly more apparent current (Amps) to deliver the same real power (Watts). If you size a wire based only on the Wattage rating of a motor without accounting for PF and efficiency, the wire will overheat. Always size motor circuits using the Full Load Amps (FLA) on the nameplate, not the calculated Watts.

Why is my 10 AWG wire limited to 30 amps if the 90°C column says 40 amps?

This is dictated by NEC 110.14(C), which governs termination temperatures. While the THHN wire insulation itself can handle 90°C, the brass lugs inside standard residential breakers and receptacles are typically only rated for 60°C or 75°C. The NEC requires you to size the overcurrent protection based on the lowest temperature rating in the entire circuit chain. For standard 15A, 20A, and 30A residential receptacles and breakers, that weakest link is almost always the 60°C column, capping 10 AWG at 30A.

Is there an exact AWG to amps formula for aluminum wire?

There is no direct mathematical formula to convert copper AWG to aluminum AWG. Aluminum has a higher electrical resistance and different thermal expansion properties than copper. To find the ampacity for aluminum, you must use the specific aluminum columns in NEC Table 310.16. As a general field rule of thumb, aluminum wire must be sized two AWG sizes larger than copper for the same amperage (e.g., to carry 100 Amps, you use 3 AWG copper, but you must step up to 1 AWG aluminum). Always use anti-oxidant compound (like Noalox) on aluminum terminations to prevent galvanic corrosion and high-resistance heating.