Electrical

Watts to Amps Calculator

Convert electrical power (Watts) to current (Amps) for DC, single-phase AC, and three-phase AC systems.

Formula I = P / VReviewed Sep 8, 2026

The Watts to Amps Calculator computes the electrical current (Amps) flowing through a circuit given the power (Watts) and the voltage (Volts). It supports Direct Current (DC) as well as Alternating Current (AC) systems including single-phase and three-phase circuits. For AC systems, the power factor must be provided to account for reactive loads.

Calculation Bench

System Type

01Power

P · The actual power consumed or generated by the circuit.

02Voltage

V · The electric potential difference. Can be line-to-line (VL) or line-to-neutral (VN).

Solution

Enter the required values to calculate the current.

I = P / V

Formula Sheet

I = \frac{P}{V}

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

I = \frac{P}{\sqrt{3} \, V_L \, PF}

I = \frac{P}{3 \, V_N \, PF}

ICurrent
PReal Power
VVoltage
PFPower Factor

Variables & Units

Symbol	Variable	Description	Common Units
I	Current	The flow of electrical charge.	A, mA
P	Real Power	The actual power consumed or generated by the circuit.	W, kW, MW
V	Voltage	The electric potential difference. Can be line-to-line (VL) or line-to-neutral (VN).	V, kV
PF	Power Factor	Ratio of real power to apparent power (cos φ). Enter as a decimal from 0 to 1.

How to Use This Calculator

01Select the electrical system type: DC, AC Single-Phase, or AC Three-Phase.
02For three-phase systems, choose whether you are using line-to-line or line-to-neutral voltage.
03Enter the power in Watts (or kilowatts, megawatts, etc.).
04Enter the voltage of the system.
05For AC systems, enter the Power Factor (a decimal between 0 and 1). For resistive loads like heaters, use 1.0.
06The calculator will instantly display the resulting current in Amps.
07For breaker or wire sizing, use the calculated current as the starting load current only. Then apply continuous-load factors, conductor ampacity rules, ambient corrections, and local electrical code requirements.

How the Formula Works

In a Direct Current (DC) circuit, power is simply the product of voltage and current (P = V × I). Therefore, current is power divided by voltage.

In Alternating Current (AC) circuits, the voltage and current can be out of phase due to inductive or capacitive loads. The Power Factor (PF) represents this phase difference (PF = cos φ).

For AC single-phase circuits, the formula incorporates the power factor: I = P / (V × PF).

For AC three-phase circuits, the power delivery is more constant and is determined by whether the voltage is measured line-to-line (using a √3 multiplier) or line-to-neutral (using a multiplier of 3).

Worked Example 01

Household Space Heater (AC Single-Phase)

Known

Power: 1500 W
Voltage: 120 V
Power Factor: 1.0

Formula

I = P / (V × PF)

Substitution

I = 1500 / (120 × 1.0)

Result

12.5 A

A standard 1500-watt resistive space heater on a 120V residential circuit will draw exactly 12.5 amps of current.

Worked Example 02

Three-Phase Industrial Motor

Known

Power: 10,000 W
Line-to-Line Voltage: 480 V
Power Factor: 0.85

Formula

I = P / (√3 × VL × PF)

Substitution

I = 10000 / (√3 × 480 × 0.85)

Result

14.15 A

An industrial motor drawing 10 kW at 480V with a power factor of 0.85 will have a line current of approximately 14.15 amps per phase.

Applications

01Determining the current draw of household appliances to check circuit breaker limits.
02Sizing electrical wiring for industrial machinery and motors.
03Calculating the output current of generators and power supplies.

Assumptions

01Assumes steady-state conditions without transient spikes.
02Assumes the load is balanced for three-phase calculations.
03Assumes a purely sinusoidal waveform for AC calculations.

Where This Model Stops

01Does not account for harmonic distortion in non-linear loads.
02Does not calculate required wire gauge or breaker size; always consult local electrical codes (e.g., NEC) for sizing.
03Motor nameplates, inrush current, duty cycle, and continuous-load rules can require larger conductors or breakers than a simple watts-to-amps conversion suggests.

Frequently Asked Questions

What is power factor and why do I need it?

Power factor (PF) is the ratio of real power (used to do work) to apparent power (total power supplied) in an AC circuit. It accounts for the phase shift between voltage and current caused by inductive or capacitive loads. For purely resistive loads like heaters or incandescent bulbs, the PF is 1.0. For motors and transformers, it is typically between 0.8 and 0.95.

Can I use this calculator to size my wires and breakers?

No. While this calculator gives the exact operating current, electrical codes (like the NEC) require you to multiply continuous loads by 125% and consider factors like wire insulation temperature ratings, conduit fill, and ambient temperature when sizing wires and breakers.

How is this different from the Circuit Breaker Size Calculator?

Watts to Amps converts power into operating current. The Circuit Breaker Size Calculator starts from load current and applies sizing logic such as continuous-load margin, so it is the better next step when selecting a breaker.

How do I convert kW to Watts for this calculator?

1 kilowatt (kW) equals 1000 Watts. You can use the unit dropdown next to the Power input to select 'kW' directly, and the calculator will handle the conversion automatically.

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