Electrical Fundamentals Calculators

Ohm's law, AC and DC circuit, single-phase and three-phase calculators with formulas and worked examples, plus related power and energy conversions.

These are the building blocks: the relations between voltage, current, resistance and power, how reactance and impedance behave on AC, and how single-phase and three-phase quantities relate. Use them to check a hand calculation, to find a missing value from two known ones, or to move between line and phase values on a three-phase system. Every calculator shows its formula and working and has unit selectors. For plain unit conversion with no circuit involved (kW to HP, kWh to joules, volts to kV), use the Conversion Centre.

Where to start

Watts, Volts, Amps, Ohms (any two): Find the two unknowns from any two of voltage, current, resistance and power.
Current from Power (kW to Amps): Line current of a three-phase load from kW, voltage and power factor.
Series RLC Impedance: Impedance, phase angle and power factor of a series R-L-C circuit.
Line and Phase Quantities (Star / Delta): Convert between line and phase quantities for star and delta connections.

All 29 calculators in this category

Ohm's Law

Ohm's Law: Find current and power from voltage and resistance. Open in Elecmetric
Power from Voltage and Current: Power and resistance from voltage and current.
AC Ohm's Law (Phasors): Enter any two of voltage, current and impedance, each with a phase angle. The third phasor and the power triangle are calculated. Open in Elecmetric
Watts, Volts, Amps, Ohms (any two): Enter any two of voltage, current, resistance and power. The other two are calculated.
Joules, Volts, Charge and eV (any two): Enter any two of energy, voltage and charge. The third is calculated: joules to volts, volts to joules, eV to volts, volts to eV.

Three Phase

Current from Power (kW to Amps): Calculate line current from real power, voltage and power factor.
kVA to Amps: Calculate line current from apparent power and voltage.
Power, Voltage, Current with Power Factor (solve any): Enter any two of power, voltage and current, with the power factor. The third is calculated, for single or three-phase AC.
Amps to kW: Real power from line current, voltage and power factor, with optional efficiency for output (shaft) power.
Amps to kVA: Apparent power from line current and voltage.
Three-Phase Power: Real, apparent and reactive power from voltage, current and power factor. Open in Elecmetric
Line and Phase Quantities (Star / Delta): Phase voltage, phase current and per-phase impedance from line values and the winding connection. Open in Elecmetric
Neutral Current from Unbalanced Load: Neutral current and percentage unbalance for three phase currents of any size. Open in Elecmetric
Three-Phase Voltage Unbalance: Percentage voltage unbalance from the three line-to-line voltages, as used for motor derating. Open in Elecmetric

DC Circuits

Resistors in Series: Total resistance of up to three resistors in series. Open in Elecmetric
Resistors in Parallel: Equivalent resistance of up to three resistors in parallel. Open in Elecmetric
Delta to Star Resistance Conversion: Equivalent star resistors for a delta network of three resistors. Open in Elecmetric

AC Circuits

Inductors in Series and Parallel: Combined inductance of three inductors, both ways. Open in Elecmetric
Inductive and Capacitive Reactance: Reactance of an inductor and a capacitor at a given frequency. Open in Elecmetric
Series RLC Impedance: Impedance, phase angle and power factor of a series R-L-C circuit. Open in Elecmetric
Frequency and Period: Period and angular frequency from frequency. Open in Elecmetric
RMS, Peak and Peak-to-Peak: RMS and peak-to-peak voltage of a sine wave from its peak. Open in Elecmetric
LC Resonance and Q Factor: Resonant frequency, reactance at resonance and Q of a series RLC circuit. Open in Elecmetric
Energy in a Capacitor and an Inductor: Energy stored in a charged capacitor and in a current-carrying inductor. Open in Elecmetric

Single Phase

Watts to Amps: Current drawn by a single-phase or DC load from watts and voltage.
Amps to Watts: Real power of a single-phase or DC load from current and voltage.

Converters and Units

HP to kW and kW to HP: Convert mechanical horsepower, metric horsepower and kilowatts. Open in Elecmetric
Power Unit Converter (W, kW, MW, HP, PS): Convert real power between watts, kilowatts, megawatts and horsepower: watts to kW, kW to watts, MW to kW. Open in Elecmetric
Energy Unit Converter: Convert between kWh, MJ, kcal, BTU and joules. Open in Elecmetric

What these calculators do not cover

These are idealised circuit relations. They assume sinusoidal waveforms and lumped components, and balanced loads unless a calculator says otherwise. They do not model harmonics, cable effects or protection. Use the cable, protection and power systems categories for design checks.

Cross-check: all 29 calculators listed here are compared with 515 reference calculations written separately from the engine. This confirms the arithmetic and selection rules. It does not confirm that a standard table or convention matches your standard or manufacturer data.

Related categories

Power and Energy Cable Engineering Electronics and Instrumentation Engineering Mathematics Scientific Calculator All engineering calculators Conversion Centre