Watts to Amps Calculator
Convert electrical power in watts or kilowatts to current in amps for DC, single-phase AC, and three-phase AC circuits.
Calculator Inputs
Current Result
How to use this calculator
- Select the circuit type. Choose direct current (DC), single-phase AC, or three-phase AC depending on your power source.
- Enter the power and voltage. Type the power value in watts (W) or kilowatts (kW), followed by the supply voltage in volts (V).
- Set the power factor (AC only). For AC circuits, enter the load's power factor between 0.1 and 1.0 (defaulting to 1.0 for resistive loads).
- Read the current. The calculator displays the current in amps (A) immediately.
Make sure you select the right unit for power. Entering 5 kW as 5 W will give a current one thousand times too small. If you know apparent power in kVA rather than watts, convert it first with our kVA to kW calculator, or reverse the calculation using the amps to watts calculator.
Formulas
The relationship between power, voltage and current depends on whether the system is DC, single-phase AC, or balanced three-phase AC:
| System | Formula | Description |
|---|---|---|
| DC | I = P / V | Power divided by DC voltage |
| Single phase AC | I = P / (V × PF) | Power divided by voltage times power factor |
| Three phase AC | I = P / (√3 × V × PF) | Power divided by √3 times line-to-line voltage times power factor |
Common mistakes
- Using phase-to-neutral voltage instead of line-to-line voltage in the three-phase formula.
- Assuming a power factor of 1.0 for inductive loads like pumps or compressors, which causes you to underestimate current.
- Forgetting to convert kilowatts to watts (1 kW = 1,000 W) when calculating manually.
- Confusing real power in watts with apparent power in volt-amps.
Worked Example
1. Single-phase domestic appliance
A 2,300 W electric heater runs on a 230 V single-phase supply with a resistive power factor of 1.0.
- Formula: I = P / (V × PF)
- Calculation: I = 2,300 / (230 × 1.0) = 10 A
2. Three-phase industrial motor
A 10 kW three-phase motor connects to a 400 V line-to-line supply with a measured power factor of 0.9.
- Formula: I = P / (√3 × V × PF)
- Calculation: I = 10,000 / (1.73205 × 400 × 0.9) = 10,000 / 623.54 ≈ 16.04 A
3. Low-voltage DC solar circuit
A 120 W LED floodlight operates on a 12 V DC battery bank.
- Formula: I = P / V
- Calculation: I = 120 / 12 = 10 A
Once you calculate the circuit current, use our voltage drop calculator to size the cable for your run distance and verify that the voltage at the load remains within acceptable limits.
Frequently Asked Questions
What is the formula to convert watts to amps for DC circuits?
For DC circuits, divide the power in watts by the voltage: I = P / V. For instance, a 120 W load on a 12 V battery draws 10 A.
Why does AC conversion require a power factor?
In alternating current circuits with inductive or capacitive components, voltage and current waveforms can be out of phase. The power factor (PF) accounts for this phase difference, representing the ratio of real working power to total apparent power.
What power factor should I enter if I do not know it?
For resistive equipment like electric heaters or incandescent lights, the power factor is 1.0. For typical electric motors, transformers, or general inductive loads, 0.8 to 0.9 is a common operating estimate.
Which voltage do I enter for a three-phase system?
Enter the line-to-line RMS voltage (such as 400 V or 480 V), not the phase-to-neutral voltage. The three-phase formula already incorporates the square root of 3 (approximately 1.732) to relate line-to-line voltage to line current.
Can I convert kilowatts directly with this calculator?
Yes. The calculator accepts power in either watts (W) or kilowatts (kW). It automatically converts kilowatts to watts before evaluating the formula.
How does current affect cable sizing?
The current in amps determines how much heat the conductor produces and how much voltage will be lost along the run. Sizing a cable requires checking both thermal current capacity and allowable voltage drop.
Disclaimer
This calculator is provided for educational and estimation purposes only. Always consult a licensed electrical professional and adhere to your local electrical codes and standards before making any decisions based on these calculations.
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