Watts to Amps Calculator (AC, DC, 3-Phase)

How the number is made

How to use this calculator

Type the watts and the volts. Choose DC, single-phase AC, or three-phase AC. For AC, set the power factor. The current appears in the result card, with the steps beside it. Submit the form if JavaScript is off. The same formulas run on the server, so the first number is already on the page.

For AC, enter RMS values from the same operating condition. The three-phase model requires a balanced load and line-to-line RMS voltage. Power factor is real power divided by apparent power, not efficiency. Do not guess an unknown factor: using 1 gives the lowest current for fixed watts and volts, not a safe installation value.

The formulas

DC: I = P / V

I = \frac{P}{V}

Single-phase AC: I = P / (V × PF)

I = \frac{P}{V \times PF}

Three-phase AC: I = P / (√3 × V × PF)

I = \frac{P}{\sqrt{3} \times V \times PF}

P is watts, V is volts, I is amps, and PF is the power factor. For DC, current is power divided by voltage. For single-phase AC, real power also depends on power factor. For a balanced three-phase load, use line-to-line RMS voltage and line RMS current with the power-factor term. The source list below documents these formula scopes; the three-phase equation does not cover unbalanced loads.

DC

Direct current has no power factor. A 12 V circuit and a 120 V circuit with the same watts do not draw the same amps. Lower voltage means higher current. That is why a low-voltage run often needs larger wire even when the watts look small. The DC choice ignores whatever power factor is typed in the form, and the steps say so.

Single-phase AC

At a power factor of 1, single-phase amps match the DC formula for the same power and voltage. At 0.8, the calculated current is higher because the denominator is smaller. Use a documented power factor for the same operating point. The answer does not establish a conductor or protective-device rating.

Three-phase

Three-phase current is lower than single-phase current for the same watts, volts, and power factor, because the square root of 3 is in the denominator. The volts have to be the line-to-line value. If you type the phase-to-neutral voltage by mistake, the amps come out high. This page does not convert 120 V to 208 V for you. Type the voltage you are actually using.

Worked example

Type 1800 watts, 120 volts, single-phase, power factor 1. The engine returns 15 amps. The step is 1800 divided by 120. Nothing else is added. Change the power factor to 0.8 and the current rises, because the formula divides by 0.8 as well. Change the circuit to three-phase and type the line-to-line voltage if that is the system you have. The reference table below is the same engine at power factor 1, single-phase, for a set of round watt values. It is not a list of appliance ratings.

What this page does not do

This tool does not select a wire, breaker or generator, and does not apply motor starting current, installation rules or efficiency. Use input power, not output power. Shareable calculations include your values in the page address, which may also appear in browser history and server logs. Do not enter confidential information. The clean calculator address remains the canonical page.

Amps at 120 V and 240 V

Single-phase, power factor 1. Every cell is computed by the same function as the result card.

Watts	Amps at 120 V	Amps at 240 V
100	0.8333	0.4167
250	2.0833	1.0417
500	4.1667	2.0833
750	6.25	3.125
1000	8.3333	4.1667
1200	10	5
1500	12.5	6.25
1800	15	7.5
2000	16.6667	8.3333
2400	20	10
3000	25	12.5
3600	30	15
4800	40	20
5000	41.6667	20.8333

Common questions

How do I convert watts to amps at 120 volts?

Divide watts by 120 for DC, or for single-phase AC at a power factor of 1. If the power factor is lower, divide by 120 times that power factor. The table on this page already did the power-factor-1 case.

Does power factor change the amps?

Yes. Single-phase AC uses I = P / (V × PF). Balanced three-phase AC uses I = P / (√3 × V_LL × PF). For fixed power, voltage and circuit type, a power factor of 1 gives the smallest current within that model. DC does not use power factor.

How do I convert watts to amps for three-phase?

Divide watts by the square root of 3, then by the line-to-line volts, then by the power factor. Do not use the single-phase formula on a three-phase load.

Is the DC result the same as single-phase AC at power factor 1?

Yes, for the same watts and voltage. Both use watts divided by volts. Balanced three-phase AC also divides by √3 and uses line-to-line voltage, so it is not the same result. The steps retain the selected circuit assumption.

Where does the wire size come from?

This page converts power to current; it does not select a conductor or protective device. A calculated current alone does not establish an installation size. Conductor design requires a qualified review using the applicable rules and equipment conditions.

For an installation voltage-drop result, gather the complete run details for a qualified review; the voltage-drop review guide does not calculate a conductor or installation result.

How to read a shared result

A shared address preserves watts, volts, circuit and power factor. The server calculates those inputs even without JavaScript; enhanced calculations update the same result in place. The clean canonical address identifies the calculator, not your particular scenario.

Results are rounded to four decimal places: 5000 watts at 240 volts and power factor 1 gives 20.8333 amps. The table uses the same rounding. This is an explanatory calculation, not a precision measurement or a method for choosing installation wiring.

Keep the assumptions with the number. A current without the voltage, the circuit, and the power factor cannot be checked later. The card lists those four items above the steps so a printed page still shows them. The print button hides the menu and the form. The steps stay.

Watts and volt-amperes

Watts describe real power; volt-amperes describe apparent power. Do not enter a VA rating as watts or assume an unknown power factor is 1. Use the equipment documentation and a tool that matches the quantity you know. None of these conversions establishes a conductor size or installation approval.

Wattopedia Editorial Team. Formula scope and sources are listed above.

Convert watts to amps using real electrical input power and voltage. An illustrative 1500 watt single-phase load at 120 volts and power factor 1 draws 12.5 amps. Three-phase results require a balanced load and line-to-line RMS voltage.

Direct current

For steady DC, current is watts divided by volts. A hypothetical 1500 watt load at 12 volts draws 125 amps. This is an arithmetic example, not an equipment rating. Use input power and voltage from the same operating condition. DC does not use power factor. If voltage falls while input power stays constant, calculated current rises. That constant-power assumption matters: the equation does not predict how an actual device responds to a different voltage. It does not estimate battery sag or establish equipment compatibility.

Single-phase

For sinusoidal single-phase AC, divide real watts by RMS volts and power factor. At power factor 1, the illustrative 1500 watt input gives 12.5 amps at 120 volts or 6.25 amps at 240 volts. These are separate scenarios with the same power and power factor, not instructions to change an equipment supply. At 120 volts and power factor 0.8, the result is 15.625 amps. Apparent power in volt-amperes is RMS volts times RMS amps; it does not include a power-factor multiplier. Do not enter a VA rating as real watts. Obtain a documented power factor rather than guessing one.

Balanced three-phase

Enter total real electrical input power, line-to-line RMS voltage and power factor for a balanced sinusoidal load. Current is watts divided by the square root of 3, line-to-line volts and power factor. A hypothetical 1500 watt total load at 208 volts and power factor 0.9 gives 4.6262 amps of line current. Do not add the currents of three conductors or substitute phase-to-neutral voltage. Unbalanced loads and distorted waveforms are outside this model. Output power and motor efficiency are not interchangeable with electrical input power and power factor. The result does not apply a starting-current factor.

What the current does not decide

This tool checks a power-to-current calculation. It does not select conductors, protective devices or equipment, or assess an installation. Keep the circuit, voltage and power factor with the result so the arithmetic can be checked. Results use four decimal places; values too small to represent as positive results are refused rather than shown as zero. Shared calculation addresses include inputs and may appear in browser history and server logs. Do not enter confidential information. Sources explain the formula conditions, not an approval to install equipment.

Reader questions

Does a lower power factor raise the current?

For fixed real power and RMS voltage, yes. At 1500 watts and 120 volts, power factor 0.8 gives 15.625 amps instead of 12.5 amps at power factor 1. This compares stated conditions, not an unknown appliance.

Why does the same power draw a different current at another voltage?

At fixed real power and power factor, current is inversely proportional to voltage. An illustrative 1500 watts is 6.25 amps at 240 volts and power factor 1, or 125 amps at 12 volts DC. These calculations do not establish equipment compatibility or installation requirements.