Watts to Amps Calculator

Convert watts to amps at any voltage with instant results for DC, AC single-phase, and AC three-phase circuits. Use it to size breakers, check circuit capacity, or verify that an appliance will not overload your wiring.

Power (Watts)

Voltage

Circuit Type

Voltage Reference

Power Factor

= 12.5 amps

1,500W ÷ 120V = 12.5A

See full breakdown for 1,500W at 120V

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What Is Watts to Amps?

Watts measure power (how much energy an appliance uses per second). Amps measure current (how much electricity flows through the wire). To convert between them, you need the voltage. The formula is Amps = Watts ÷ Volts for DC circuits.

This conversion is essential for electrical sizing: determining which breaker to use, what wire gauge is needed, and whether a circuit can handle a given appliance. A 1500W space heater on a 120V circuit draws 12.5 amps. That same 1500W on a 240V circuit draws only 6.25 amps.

The Formulas

DC (Direct Current)

Amps = Watts ÷ Volts

Used for battery circuits, solar panels, and automotive systems. No power factor involved.

AC Single Phase

Amps = Watts ÷ (Volts × Power Factor)

Used for standard residential circuits (120V and 240V). Power factor is typically 0.85 for mixed loads, 1.0 for resistive loads (heaters), and 0.65-0.80 for motors.

AC Three Phase

Amps = Watts ÷ (Volts × √3 × Power Factor)

Used for commercial and industrial equipment at 208V, 240V, or 480V. The √3 factor (1.732) accounts for the three-phase power distribution.

Why Voltage Matters

The same wattage draws very different amperage depending on the voltage. A 1500W space heater at 120V draws 12.5A, which sits within a single amp of the 80% continuous-load allowance on a standard 15A branch circuit under NEC 210.19(A). The same heater at 240V draws only 6.25A. This is why large US appliances like dryers, ranges, water heaters, and EV chargers typically use 240V dedicated circuits: the same real power rides on lower current, which generally reduces I²R loss over the run and often allows a smaller conductor and overcurrent device for the same duty. Actual conductor and OCP sizing still depends on the appliance nameplate, cable type, termination temperature, and local code.

Power Factor Explained

Power factor measures how efficiently AC power is used. Resistive loads (heaters, incandescent bulbs) have a power factor of 1.0. Inductive loads (motors, transformers) have a lower power factor (typically 0.80-0.85), meaning they draw more amps than the DC formula predicts.

Load Type	Typical PF	Example
Resistive (heaters, incandescent)	1	12.5A for 1500W at 120V
Fluorescent lamps	0.95	13.16A for 1500W at 120V
LED lighting	0.9	13.89A for 1500W at 120V
Synchronous motors	0.9	13.89A for 1500W at 120V
Typical mixed loads	0.85	14.71A for 1500W at 120V
Induction motors (full load)	0.8	15.63A for 1500W at 120V
Computers (without PFC)	0.65	19.23A for 1500W at 120V
Induction motors (no load)	0.35	35.71A for 1500W at 120V

For most residential calculations, use PF 1.0 (resistive) or PF 0.85 (mixed). Do not use typical values for precise engineering.

Quick Results Table

Each column uses the primary interpretation for its voltage so the table lines up with the result pages: 12V as DC, 120/230/240V as AC single-phase at PF 1.0 resistive, 208/480V as AC three-phase L-L at PF 0.85. Three-phase cells show the line current (what a clamp meter reads on one conductor) for a given total real power in the Watts column. Click any cell for the full breakdown.

Watts	12V DC	120V 1Φ PF 1.0	208V 3Φ L-L PF 0.85	230V 1Φ PF 1.0	240V 1Φ PF 1.0	480V 3Φ L-L PF 0.85
100W	8.33A	0.8333A	0.3266A	0.4348A	0.4167A	0.1415A
200W	16.67A	1.67A	0.6531A	0.8696A	0.8333A	0.283A
500W	41.67A	4.17A	1.63A	2.17A	2.08A	0.7075A
750W	62.5A	6.25A	2.45A	3.26A	3.13A	1.06A
1,000W	83.33A	8.33A	3.27A	4.35A	4.17A	1.42A
1,200W	100A	10A	3.92A	5.22A	5A	1.7A
1,500W	125A	12.5A	4.9A	6.52A	6.25A	2.12A
1,800W	150A	15A	5.88A	7.83A	7.5A	2.55A
2,000W	166.67A	16.67A	6.53A	8.7A	8.33A	2.83A
3,000W	250A	25A	9.8A	13.04A	12.5A	4.25A

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Frequently Asked Questions

How do I convert watts to amps? expand_more

Divide watts by volts: Amps = Watts ÷ Volts (DC). For AC circuits, also divide by the power factor: Amps = Watts ÷ (Volts × PF). For example, 1500W at 120V is 12.5A (DC).

Why does voltage matter for the conversion? expand_more

The same wattage draws different amps at different voltages. 1500W at 120V is 12.5A, but at 240V it is only 6.25A. Higher voltage means lower current for the same power.

What is power factor and when does it matter? expand_more

Power factor (PF) measures how efficiently AC power is used. Resistive loads like heaters have a PF of 1.0. Motors typically have 0.80-0.85. For DC circuits, power factor does not apply.

What is the difference between single-phase and three-phase? expand_more

Single-phase uses one AC waveform and is the standard residential supply. Three-phase uses three waveforms offset by 120 degrees and is the standard commercial and industrial panel configuration. At a given apparent power, three-phase distributes the current across three line conductors instead of one, so each line carries less current per conductor than the single-phase equivalent at the same line-to-line voltage, which is why commercial panels and large motors use three-phase distribution. The exact amp figures depend on whether the voltage cited is line-to-line or line-to-neutral and on the load's power factor, so see the three-phase formula above for the details.

How many amps can a 15-amp breaker handle? expand_more

NEC 210.19(A) sizes the conductor and overcurrent device at not less than 125% of any continuous load (a load that runs three hours or more), which is equivalent to saying a continuous load cannot exceed 80% of the breaker rating. For a 15A breaker, that works out to 12A of continuous current, or 1,440W at 120V. Non-continuous loads can use the full 15A at 1,800W.

This calculator provides estimates for reference purposes only. Always consult a licensed electrician and verify compliance with the National Electrical Code (NEC) and local electrical codes before performing any electrical work.

Standards & References

This page cites the following electrical codes and standards. Always consult the current edition of your local adopted standard for authoritative requirements.

NEC Table 310.16. Allowable ampacities of insulated conductors rated up to 2000V, 60°C through 90°C, not more than three current-carrying conductors in raceway or cable.
National Electrical Code (NFPA 70), Article 310, Conductors for General Wiring. Reference →
NEC 240.4(D). Small conductor rule: overcurrent protection shall not exceed 15A for 14 AWG, 20A for 12 AWG, and 30A for 10 AWG copper, regardless of ampacity table values.
National Electrical Code (NFPA 70), Article 240, Overcurrent Protection. Reference →
IEC 60038. IEC standard voltages. Defines 230/400V as the nominal low-voltage supply for 50Hz systems, which harmonized European residential supply in 1995.
International Electrotechnical Commission. Reference →

Disclaimer: The information on this page is provided for reference. Always consult a licensed electrician and the current edition of your local adopted electrical code before performing electrical work.