What formula does this calculator use?

DC: P = V × I. Single-phase AC: P = PF × V × I. Three-phase AC: P = √3 × PF × V × I (where √3 ≈ 1.7321). Power factor (PF) accounts for the phase difference between voltage and current in AC circuits.

What is power factor and why does it matter for AC?

Power factor is a number between 0 and 1 that describes how efficiently current is converted to real (useful) power. Resistive loads such as heaters have PF = 1. Motors, transformers, and fluorescent lights often have PF between 0.7 and 0.95. Using PF = 1 for AC gives apparent power (VA), not real power (W).

What voltage should I use for three-phase calculations?

Enter the line-to-line (phase-to-phase) voltage for three-phase circuits. In North America this is typically 208 V, 240 V, or 480 V. The formula P = √3 × PF × V × I already accounts for the three-phase relationship.

How accurate is this calculator?

Results are accurate for steady-state, balanced loads using the standard formulas. Real-world power may differ slightly due to harmonic distortion, load imbalance, or measurement tolerances. For precision engineering work always verify with calibrated instruments.

Can I convert watts back to amps?

Yes — rearrange the formula: I = P / V (DC), I = P / (PF × V) (single-phase AC), or I = P / (√3 × PF × V) (three-phase AC). Our Ohm's Law Calculator on this site can also help with related conversions.

Amps to Watts Calculator

Name: Amps to Watts Calculator
Availability: InStock
Author: Nham Vu

Enter current (amps) and voltage — plus power factor for AC — to instantly calculate power in watts for DC, single-phase AC, or three-phase AC circuits.

Amps to Watts

Circuit Type

Current — I

Voltage — V

Power Factor — PF (0 to 1)

P = V × I (DC)

Power Result

Enter current and voltage, then click Calculate.

P = V × I

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Summary

Enter current (amps) and voltage — plus power factor for AC — to instantly calculate power in watts for DC, single-phase AC, or three-phase AC circuits.

How it works

Select the circuit type: DC, AC Single-Phase, or AC Three-Phase.
Enter the current in amps (A).
Enter the voltage in volts (V).
For AC circuits, enter the power factor (0 to 1). DC circuits use PF = 1 automatically.
Click Calculate to see the result in watts (W) and kilowatts (kW).
Click Reset to clear the form and start over.

Use cases

Calculate how many watts a household appliance draws from its rated current.
Size circuit breakers and fuses based on load current and voltage.
Estimate generator or UPS capacity needed for a given amp draw.
Convert panel amperage to total wattage for electrical load planning.
Check three-phase motor power consumption from nameplate current.
Verify solar-panel array output when current and voltage are known.
Determine power consumption of DC systems like automotive or marine electronics.
Cross-check results when designing LED driver or power supply circuits.

Frequently Asked Questions

Last updated: 2026-06-09 · Reviewed by Nham Vu