Electrical Power Calculator | Watts, Volts & Amps

Calculate electrical power in watts from voltage and current

Solve DC, AC single-phase, and 3-phase circuits Find your electricity cost from watt usage...

When Should You Use This Calculator?

Calculating appliance power (e.g., toaster 120V 10A = 1.2 kW)
Estimating energy cost from watts, hours, and $/kWh
Three-phase motor or industrial load power with power factor
Solving for power from any two of voltage, current, or resistance

How to Use This Calculator

Select DC or AC (single- or three-phase), then pick which two values you know (V&I, I&R, or V&R).
For AC, enter the power factor.
Optionally check "Calculate Energy Consumption & Cost" and add hours per day and your $/kWh rate.
Review the computed power, and daily/monthly cost if energy cost is enabled.

Key Features:

DC, single-phase AC, and three-phase AC power
Solve from V&I, I&R, or V&R; power factor for AC
Optional energy cost from usage and $/kWh
Copy results and export (JSON for guests; PDF/CSV when signed in)

Frequently Asked Questions

What is the Power Triangle?

The Power Triangle illustrates the relationship between Real Power (Watts), Reactive Power (VAR), and Apparent Power (VA). The angle between Real and Apparent power represents the Power Factor. A power factor of 1.0 means all power is usable real power.

How do I calculate electrical power in watts?

For DC circuits: P = V × I (Voltage × Current). For single-phase AC: P = V × I × Power Factor. For 3-phase AC: P = √3 × V_line × I_line × PF. Select your circuit type in this calculator for the correct formula.

How do I calculate electricity cost from watts and kWh rate?

Energy (kWh) = Power (W) × Time (hours) / 1000. Cost = kWh × electricity rate. For example, a 1,500W heater running 8 hours at $0.12/kWh: 1.5 × 8 × $0.12 = $1.44/day. Use the kWh Cost mode in this calculator to project daily, monthly, and annual costs.

What is power factor and why does it matter?

Power factor (PF) is the ratio of real power (W) to apparent power (VA). PF = 1.0 is ideal (purely resistive load). Motors, transformers, and fluorescent lights typically have PF of 0.7-0.95. A low PF means you draw more current for the same usable power, increasing losses and utility bills.

Can I export my Power Calculator calculations?

Yes. In guest mode you can export your calculations to JSON. Signing in adds PDF and CSV export. Click the export button to download your results — useful for record-keeping, sharing, or importing into other tools.

Does this calculator save my history?

Yes. Your calculation history is saved automatically. As a guest you can keep up to 50 calculations per workspace on your device. Sign in for free to keep up to 100 per workspace and access them from any device.

Is this calculator free to use?

Yes. The Power Calculator is free to use with no sign-up required. A free account adds more calculation history, multiple workspaces, and access to your saved data from any device.

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