Electrical Power Calculator — Ohm's Law · Voltage, Current, Resistance & WattsV = IR · P = VI · P = I²R · P = V²/R · Volts · Amps · Ohms · Watts
Use this free Electrical Power Calculator to instantly compute any unknown electrical circuit parameter using Ohm's Law and the fundamental electrical power formulas. Enter any two known values to automatically solve all remaining parameters across the complete Ohm's Law electrical formula set: V = I × R (voltage in Volts = current in Amps × resistance in Ohms), P = V × I (power in Watts = voltage × current), P = I² × R (power from current and resistance), and P = V² / R (power from voltage and resistance) — covering all four electrical quantities: Voltage (V) in Volts · Current (I) in Amperes · Resistance (R) in Ohms (Ω) · Power (P) in Watts (W).
Ohm's Law calculations are foundational to every area of electrical and electronics engineering, applied daily across a wide range of professional and academic contexts: DC circuit analysis & resistor network design · AC circuit power factor & impedance calculation · electrical wiring sizing & load current calculation · LED, motor & appliance power consumption estimation · solar panel, battery & inverter system sizing · PCB trace current capacity & thermal dissipation analysis. This online Ohm's Law calculator is trusted by electrical engineering students, licensed electricians, electronics hobbyists, PCB designers, Arduino and Raspberry Pi makers, solar energy installers, and electrical safety inspectors for fast, accurate voltage, current, resistance, and wattage calculations without manual formula derivation.
⚠ Electrical Safety Disclaimer: This Ohm's Law calculator is intended for educational, academic, and estimation purposes only. All calculations assume ideal resistive DC circuit conditions and do not account for AC reactance, power factor (cos φ), temperature coefficient of resistance, component tolerances, or non-linear load behavior. Never use calculated values as the sole basis for working with live electrical circuits, mains voltage (230V/110V AC), high-current systems, or safety-critical electrical installations. Always follow IEC, NEC, BS 7671, and IS 732 electrical safety standards and consult a licensed electrical engineer or certified electrician for all real-world electrical design and installation work.
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Electrical Power Calculator — Watts, Kilowatts, and What Your Bill Will Be
Electrical power is the rate at which energy is consumed or generated, measured in watts. P = VI for DC circuits; for AC circuits, apparent power (VA), real power (W), and reactive power (VAR) diverge based on the power factor of the load. A purely resistive load has power factor 1.0 — all apparent power becomes real power. An inductive motor load at power factor 0.75 means 25% of the current drawn does no useful work but still flows through conductors and increases losses. The electrical power calculator handles both DC and AC scenarios with power factor input.
Energy cost calculation transforms power into something actionable. A 100W device running for 8 hours/day consumes 0.8 kWh daily. At $0.15/kWh, that is $0.12/day or $43.80/year. Switching to a 15W LED replacement saves 85W, reducing daily consumption to 0.12 kWh and annual cost to $6.57 — saving $37.23/year. The calculator projects annual energy cost from power rating, daily usage hours, and electricity rate so appliance and system comparisons include their operating cost, not just purchase price.
Three-phase power systems used in industrial and commercial settings require a different formula: P = √3 × VL × IL × PF, where VL is line-to-line voltage and IL is line current. A 480V three-phase system with 100A line current at 0.85 power factor delivers 70.6 kW of real power. The calculator covers single-phase and three-phase configurations with delta and wye connection options, making it usable for motor sizing, panel load calculations, and generator capacity planning.