Watts, Amps & Volts Calculator
Solve real power, voltage, or current for DC, single-phase AC, and balanced three-phase AC scenarios.
Content updated August 6, 2026
This is a quantity relationship, not a wire, breaker, motor, service, protection, or electrical-safety sizing tool. Three-phase mode assumes a balanced load and line-to-line voltage with line current.
Solve one missing quantity—real power, voltage, or current—from the other two. The calculator supports DC, single-phase AC, and balanced three-phase AC while keeping power factor and phase conventions visible.
Power, voltage, and current can use scaled SI units such as kilowatts, kilovolts, or milliamps. AC results also separate apparent power and reactive-power magnitude from real watts.
The Watts, Amps & Volts formula
DC: P = V × I · single-phase AC: P = V × I × PF · balanced three-phase AC: P = √3 × VLL × IL × PFRearrange the selected equation to solve V or I; AC voltage and current are RMS values, and three-phase inputs are line-to-line voltage and line current.
Worked example
A 120 V DC load drawing 10 A uses 1,200 W. A single-phase 2.4 kW load at 240 V and 0.8 power factor draws 12.5 A.
Assumptions, rounding, and limitations
Assumptions
- DC mode uses steady voltage and current with a multiplier of one.
- AC inputs are RMS quantities and power factor describes the complete modeled load.
- Three-phase mode assumes a balanced system with line-to-line voltage and line current.
- Unit prefixes are SI decimal prefixes.
Rounding: Calculations retain JavaScript floating-point precision; displays use up to six decimal places. The phase and power-factor equations do not round intermediate results.
Limitations
- Does not model harmonics, unbalanced phases, waveform distortion, neutral current, efficiency, motor starting, demand, energy over time, or changing power factor.
- Does not size conductors, breakers, services, transformers, protection, grounding, or determine electrical-code or safe-work requirements.
Sources
- NIST Guide to the SI, Chapter 4: SI Units and Prefixes — National Institute of Standards and Technology
- Mine Power Systems — National Institute for Occupational Safety and Health
Phase and power factor change the relationship
For DC, the model uses watts = volts × amps. Single-phase AC real power also multiplies RMS voltage and RMS current by power factor.
Balanced three-phase mode uses √3 × line-to-line RMS voltage × line RMS current × power factor. That mode is not valid for an unbalanced load or for phase values entered as if they were line values.
A quantity result is not an electrical design
The result relates measured or nameplate quantities; it does not establish a continuous-load allowance, conductor ampacity, breaker size, voltage drop, fault current, motor starting current, efficiency, or code compliance.
Power factor is load-specific and can change with operating state. Use an applicable nameplate, meter, or engineering value instead of treating the example input as a recommendation.
Frequently asked questions
▶How do I calculate watts from volts and amps?
For DC, multiply volts by amps. For AC real power, also select the phase model and enter the load power factor.
▶Why does three-phase mode use square root of three?
The balanced three-phase formula uses line-to-line voltage and line current, producing the √3 multiplier. It assumes the phases are balanced.
▶What is power factor?
Power factor is real power divided by apparent power for the modeled AC load. Enter a value greater than zero and no more than one.
▶Can zero watts produce zero amps or volts?
Yes when the other divisor is positive. A zero divisor is rejected because voltage or current could not be solved uniquely.
▶Can this size a wire or circuit breaker?
No. Electrical sizing requires current standards, equipment characteristics, installation conditions, protection rules, and qualified judgment.
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Open calculator →Disclaimer: Watts, Amps & Volts Calculator results are estimates for general information and education only, and are not financial, tax, legal or medical advice. Verify important decisions with a qualified professional.