Watts to Amps Calculator: DC, Single-Phase & 3-Phase

To convert watts to amps, you must know the voltage and electrical system. Select DC, single-phase ACあるいは balanced three-phase AC in the calculator, then enter the known power and voltage. For an AC load, also enter the power factor shown on the equipment data or project documentation.

The three core relationships are:

電気システム	Watts-to-amps formula	Voltage to enter
DC	`I = P / V`	DC voltage across the load
単相交流	`I = P / (V × PF)`	RMS voltage across the load
Balanced three-phase AC	`I = P / (√3 × VLL × PF)`	RMS line-to-line voltage

次の場合：

I is current in amperes (A);
P is real electrical power in watts (W);
V is DC or single-phase voltage in volts (V);
VLL is three-phase line-to-line voltage;
力率 is the AC power factor, expressed from 0 to 1.

Watts alone are not enough to determine amps. The same power draws more current at a lower voltage, and an AC load with a lower power factor draws more current for the same real power.

How to Use the Watts to Amps Calculator

Select DC, single-phase AC, or three-phase AC.
Choose watts and volts as the two known quantities.
Enter the real power. Convert kilowatts to watts by multiplying by 1,000 if the input field is set to watts.
Enter the operating voltage. For three-phase calculations, use line-to-line voltage.
Enter the equipment’s stated power factor for an AC load.
Read the current result and the displayed substitution before using it in another calculation.

The result is the calculated steady-state current for the entered conditions. It is not automatically a cable ampacity, circuit-breaker rating, contactor rating, or motor starting current.

Watts to Amps Formulas Explained

DC Watts to Amps

For a DC load:

I = P / V

A 480 W DC load operating at 24 V draws:

I = 480 / 24 = 20 A

This relationship is consistent with the International System of Units: the National Institute of Standards and Technology (NIST) states that one volt equals one watt per ampere.

Single-Phase AC Watts to Amps

For a single-phase AC load using real power:

I = P / (V × PF)

A 1,500 W single-phase load operating at 230 V with a stated power factor of 0.90 draws:

I = 1,500 / (230 × 0.90) = 7.25 A

If the load is purely resistive and the power factor is effectively 1, the expression reduces to I = P / V. Do not assume a power factor for a motor, drive, power supply, or other non-resistive load when manufacturer data is available.

Three-Phase Watts to Amps

For a balanced three-phase AC load using line-to-line voltage:

I = P / (√3 × VLL × PF)

A 15 kW balanced three-phase electrical load at 400 V and 0.90 power factor draws:

I = 15,000 / (√3 × 400 × 0.90) = 24.06 A

The result is approximately 24.1 A in each line, not 24.1 A divided among three conductors. This formula assumes a balanced load and line-to-line voltage. For unbalanced systems, calculate or measure the phase currents individually.

Neutral Current, Load Unbalance, and Triplen Harmonics

This watts-to-amps calculation returns balanced line current from total real power; it does not calculate neutral current. In a three-phase four-wire system, unbalanced phase-to-neutral loads produce a fundamental-frequency neutral current equal to the vector sum of the three phase currents.

Nonlinear single-phase loads require an additional check. Some switch-mode power supplies, computer equipment, and LED drivers draw distorted current containing triplen harmonics—particularly the 3rd, 9th, and 15th. These zero-sequence harmonic components can add in a shared neutral instead of cancelling, so neutral current can approach or exceed the current in an individual phase under some load combinations.

Do not estimate neutral current from total watts, average power factor, or total harmonic distortion alone. Exact assessment requires phase-resolved current magnitudes and angles, harmonic measurements, or a suitable power-quality study. Check each phase and the neutral with true-RMS instruments, and use the VIOX Harmonic and THD Calculator for preliminary harmonic screening. The calculator does not replace phase-resolved neutral-current analysis.

For a deeper explanation of the voltage definitions and phase relationship, see the VIOX guide to single-phase and three-phase power systems.

Common Watts-to-Amps Tables

These tables are quick references, not equipment ratings. Values are rounded to two decimal places.

DC Watts to Amps at 12 V, 24 V, and 48 V

パワー	12 V DC	24 V DC	48 V DC
100 W	8.33 A	4.17 A	2.08 A
500 W	41.67 A	20.83 A	10.42 A
1,000 W	83.33 A	41.67 A	20.83 A
2,000 W	166.67 A	83.33 A	41.67 A

The table represents power delivered at the stated DC voltage. A battery, converter, or inverter application may require separate allowance for conversion efficiency, operating-voltage range, and transient demand.

Single-Phase Watts to Amps at Power Factor 1

パワー	120 V AC	230 V AC	240 V AC
500 W	4.17 A	2.17 A	2.08 A
1,000 W	8.33 A	4.35 A	4.17 A
1,500 W	12.50 A	6.52 A	6.25 A
2,000 W	16.67 A	8.70 A	8.33 A
3,000 W	25.00 A	13.04 A	12.50 A

These values apply only at PF = 1. For example, 1,000 W at 120 V and PF = 0.80 は 1,000 / (120 × 0.80) = 10.42 A, not 8.33 A.

Balanced Three-Phase Watts to Amps at Power Factor 1

パワー	208 V	400 V	415 V	480 V
1 kW	2.78 A	1.44 A	1.39 A	1.20 A
5 kW	13.88 A	7.22 A	6.96 A	6.01 A
10 kW	27.76 A	14.43 A	13.91 A	12.03 A
15 kW	41.64 A	21.65 A	20.87 A	18.04 A

These are ideal PF = 1 reference values using line-to-line voltage. Enter the stated power factor in the calculator for a real AC load.

How Power Factor Changes the Amp Result

Power factor is the ratio of real power in watts to apparent power in volt-amperes. A lower power factor means the system must carry more current to deliver the same real power at the same voltage.

Consider a 5,000 W single-phase load at 230 V:

力率	Calculated current
1.00	21.74 A
0.90	24.15 A
0.80	27.17 A

The wattage does not change in this comparison; the apparent power and current do. Use measured or manufacturer-provided power factor when possible. A generic default can produce a misleading result, particularly with motors, variable-frequency drives, rectifiers, LED drivers, and switched-mode power supplies.

For conversions that start with kW or kVA, use the VIOX kW, kVA and amp calculator.

When Efficiency Belongs in the Calculation

Efficiency does not belong in every watts-to-amps formula. First determine what the stated watts represent.

Power value available	意味	Calculation approach
Electrical input watts	Real power already drawn by the equipment	Do not divide by efficiency again
Mechanical output watts or motor shaft kW	Useful output after internal losses	Divide by efficiency to estimate electrical input power
Nameplate current	Manufacturer’s rated current under stated conditions	Prefer it for final equipment selection

If a motor is rated by mechanical output power, an estimate for balanced three-phase input current is:

I = Pout / (√3 × VLL × PF × η)

配線がどこに η is efficiency expressed from 0 to 1. This equation estimates rated operating current; it does not predict starting current. When the motor nameplate provides current for the actual voltage and connection, use that value for final selection rather than replacing it with a generic calculation.

VIOX electrical formulas reference provides additional equations for low-voltage panel calculations.

Why Calculated Amps May Differ From Measured or Nameplate Current

A mathematically correct conversion can still differ from field current because the inputs or operating conditions differ. Check:

Actual voltage: supply voltage can differ from its nominal value.
Actual load: equipment may operate below or above the assumed output point.
力率: it can change with load and control mode.
効率が良い： output-rated machines require an efficiency value, and efficiency is not constant at every load point.
Phase balance: the standard three-phase equation assumes a balanced load.
Waveform distortion: nonlinear equipment can require true-RMS measurement and manufacturer data.
Neutral loading: in a three-phase four-wire system, phase unbalance and triplen harmonics from phase-to-neutral nonlinear loads can produce neutral current that the balanced line-current formula does not show.
Starting or inrush current: the steady-state power equation does not calculate a motor, transformer, or electronic-load transient.

Use a suitable meter and a safe measurement procedure when the actual operating current matters. Preserve the system type, voltage, load condition, power factor, and measurement method with the result.

Calculated Current Is Not a Breaker or Cable Size

The converted current is one input to equipment selection, not the final rating. Cable selection also depends on conductor material, insulation, installation method, ambient temperature, grouping, terminal limitations, voltage drop, and applicable wiring rules. Circuit-breaker selection additionally depends on trip behavior, breaking capacity, starting current, cable protection, coordination, system voltage, poles, and the relevant product standard.

Continue the design as separate checks:

Estimate a protective-device current rating with the circuit breaker size calculator.
Check conductor requirements with the cable size calculator.
Verify the selected route with the 電圧降下計算ツール.

Do not apply a universal “80% rule” to every result. Continuous-load requirements, equipment ratings, and installation rules depend on the governing market, code, equipment, and application.

よくある質問

How many amps is 1,000 watts?

It depends on voltage and system type. At power factor 1, 1,000 W is 83.33 A at 12 V DC, 8.33 A at 120 V single-phase, 4.35 A at 230 V single-phase, or 1.44 A at 400 V balanced three-phase. An AC power factor below 1 increases the current.

Can I convert watts to amps without knowing volts?

No. Watts do not determine current by themselves. You need voltage, and for AC real-power conversion you also need the phase arrangement and power factor.

Why does three-phase watts-to-amps use 1.732?

The value 1.732 is an approximation of √3. It appears when total power in a balanced three-phase system is expressed using line-to-line voltage and line current.

Should I include motor efficiency in a watts-to-amps calculation?

Include efficiency when the watt or kilowatt value is mechanical output power. Do not apply it again when the stated watts already represent electrical input power. Prefer the motor nameplate current for final selection.

How do I convert amps back to watts?

Rearrange the applicable equation. For DC, P = V × I. For single-phase AC, P = V × I × PF. For balanced three-phase AC, P = √3 × VLL × I × PF.

Watts to Amps Calculator for DC, Single-Phase, and Three-Phase Systems