A pure "voltage to amp converter" is a physical impossibility without a third variable. You cannot convert volts directly to amps any more than you can convert miles per hour to gallons of gas. However, if you are searching for the amperage draw of a standard 1500W resistive load (like a space heater, hair dryer, or coffee maker) on a standard US 120V branch circuit, the direct answer is 12.5 amps.

The formula used is Watt’s Law: I = P ÷ V. Substituting the baseline values: 12.5A = 1500W ÷ 120V.

Because voltage is merely the electrical pressure and amperage is the flow rate, you must know either the power consumption (Watts) or the resistance (Ohms) to complete the math. Below is the exact framework to convert your specific voltage and wattage into amps, and more importantly, how to translate that amp number into the correct breaker and wire size according to NEC-style guidance.

Neighboring Values: The 120V Amperage Chart (±20% Range)

Most household appliances fall within a 20% power band of the standard 1500W baseline. Use this reference table to find your exact amperage and the minimum required breaker size for a standard 120V single-phase circuit.

Watts (±20%) Voltage Amps (Calculated) Minimum Breaker (Non-Continuous) Minimum Breaker (Continuous >3hrs)
1200W 120V 10.0A 15A 15A
1350W 120V 11.25A 15A 15A
1500W 120V 12.5A 15A 20A (Requires 125% derating)
1650W 120V 13.75A 15A 20A
1800W 120V 15.0A 20A 20A

How the Math Shifts: 120V vs 230V vs 3-Phase

The 12.5A answer above relies on three fixed assumptions: Real Power (Watts), a Power Factor (PF) of 1.0 (purely resistive), and a Single-Phase supply. Change any of these, and the amperage shifts drastically.

The 230V Shift (EU/UK/AU or US Heavy Appliances)

If you take that same 1500W space heater and plug it into a 230V European mains supply (or a US 240V baseboard heater circuit), the current drops by nearly half.
Calculation: 1500W ÷ 230V = 6.52 Amps.
This is why high-draw appliances like dryers and EV chargers use 240V in the US; doubling the voltage halves the amperage, allowing you to use thinner, cheaper copper wire.

The 3-Phase Shift (Commercial/Industrial)

For 3-phase power, the formula expands to account for the square root of 3 (1.732) and the power factor: I = P ÷ (√3 × V × PF).
If you are sizing a 1500W (1.5kW) motor on a 208V 3-phase system with a typical 0.85 Power Factor:
Calculation: 1500 ÷ (1.732 × 208 × 0.85) = 4.9 Amps.

When the Conversion is Meaningless: If you are dealing with an inductive load (like an AC compressor, well pump, or transformer) and you do not know the Power Factor, calculating amps from Watts and Volts will give you a dangerously low number. Inductive loads draw "Apparent Power" (VA) which is higher than "Real Power" (W). Always use the FLA (Full Load Amps) stamped on the motor nameplate instead of calculating it blindly. For a deeper look at this discrepancy, refer to Fluke's guide on Power Factor.

Decision Tree: Sizing Your Breaker and Wire

Calculating the amps is only step one. Step two is selecting the correct overcurrent protection and wire gauge. The National Electrical Code (NEC) requires specific derating for continuous loads (anything running for 3 hours or more). Follow this decision path to terminate on the exact part numbers you need at the hardware store.

  • IF your calculated load is under 12A AND runs for less than 3 hours (e.g., a 1200W microwave used for 5 minutes):
    → Pick: 15A Breaker (Standard 120V) with 14 AWG Copper (THHN or 14/2 NM-B).
  • IF your calculated load is 12.5A to 16A OR runs for more than 3 hours continuously (e.g., a 1500W space heater left on all night, requiring 125% derating to 15.6A):
    → Pick: 20A Breaker (Standard 120V) with 12 AWG Copper (THHN or 12/2 NM-B).
  • IF your calculated load is over 16A on a 120V circuit (e.g., an 1800W commercial heat gun):
    → Pick: 20A Breaker with 12 AWG Copper. (Note: If the load exceeds 16A continuously, you must step up to a 30A breaker and 10 AWG wire, or move the appliance to a 240V circuit).
  • IF you are wiring a 230V/240V European or US appliance drawing under 12A:
    → Pick: 15A Double-Pole Breaker (US) or 16A MCB (EU/UK) with 14 AWG (US) or 1.5mm² (EU) copper.

Frequently Asked Questions

Can I use this logic for DC circuits like solar or cars?

Yes. DC circuits use the exact same baseline formula (I = P ÷ V) because there is no Power Factor or phase angle to worry about. A 120W LED light bar on a 12V truck battery draws exactly 10 Amps (120 ÷ 12). However, because DC voltage drops significantly over distance, you must also calculate voltage drop and often upsize your wire by one or two AWG sizes compared to AC equivalents.

What if I only know the Ohms (Resistance)?

If you have a heating element and know its resistance, drop Watt's Law and use Ohm's Law: I = V ÷ R. For example, a 120V circuit with a 10-ohm heating coil will draw 12 Amps (120 ÷ 10).

Why do motor nameplates show higher amps than my calculation?

Motors have inrush current (Locked Rotor Amps) that can be 5 to 7 times higher than their running current. Furthermore, motors are not 100% efficient; a 1500W (2 HP) motor outputting 1500W of mechanical work might draw 1900W of electrical power to overcome heat and friction losses. Always size breakers and wire based on the nameplate FLA (Full Load Amps) or LRA (Locked Rotor Amps), never on the theoretical mechanical wattage output.