Tools · Electrical Engineering
Electrical Engineering Calculators
Choose one calculator for transparent electrical arithmetic, unit checks and introductory system relationships.
Calculation logic runs locally without accounts, storage, telemetry or third-party services.
Educational reference only. Results do not approve a design, cable, protection setting, electrical installation, operating action or compliance decision. Use approved drawings, equipment data, studies, specifications and competent engineering review.
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Calculations use JavaScript numerical precision and normally display up to eight significant figures. When exactly one compatible input is blank, it is calculated and filled automatically. Validation and results are announced to assistive technology.
Ohm's law and DC power
Solve one introductory DC relationship from the entered known quantities.
V = IR; P = VI.
- Symbols and basis
- V = voltage in volts; I = current in amperes; R = resistance in ohms; P = power in watts.
The relationship assumes the stated operating condition can be represented by the entered values; it does not assess wiring, temperature rise or protection.
Series and parallel resistance
Find equivalent resistance for two or three ideal resistors in one series or parallel group.
Rseries = R₁ + R₂ + ...; 1 / Rparallel = 1 / R₁ + 1 / R₂ + ...
- Symbols and basis
- R = resistance in ohms. At least two positive resistor values are required; a blank third value is ignored.
This does not model source impedance, cable resistance, temperature, tolerance, non-linear elements or a full circuit.
Electrical energy
Convert a constant power and operating duration into watt-hours and kilowatt-hours.
E = Pt.
- Symbols and basis
- E = energy; P = constant power in watts; t = duration in hours.
This calculation assumes constant entered power and does not calculate demand, tariffs, losses, duty cycles or battery condition.
Single-phase power
Calculate ideal single-phase kW, kVA or current from compatible RMS quantities.
S = VI / 1000; P = VI PF η / 1000.
- Symbols and basis
- V = RMS voltage; I = RMS current; PF = power factor; η = efficiency. Power is displayed in kW or kVA.
Use only where the waveform, load and values are represented by the selected simplified relationship.
Three-phase power
Calculate balanced three-phase kW, kVA or current using line-to-line voltage and line current.
S = √3 VI / 1000; P = √3 VI PF η / 1000.
- Symbols and basis
- V = line-to-line RMS voltage; I = line current; PF = power factor; η = efficiency. The load is assumed balanced.
This relationship does not model unbalance, harmonics, starting current, fault level, generator loading limits or equipment ratings.
Power triangle
Relate real, reactive and apparent power for a compatible sinusoidal steady-state condition.
S² = P² + Q²; PF = P / S.
- Symbols and basis
- P = real power in kW; Q = reactive power in kVAr; S = apparent power in kVA; PF = power factor.
This does not represent harmonic distortion, tariff treatment, power-factor correction requirements or equipment loading limits.
Reactance and impedance
Calculate ideal inductive or capacitive reactance, then an impedance magnitude from entered resistance and reactance values.
XL = 2πfL; XC = 1 / (2πfC); |Z| = √(R² + (XL − XC)²).
- Symbols and basis
- f = frequency in hertz; L = inductance in mH; C = capacitance in µF; R, X and |Z| are in ohms.
This is a single-frequency idealised relationship. It does not model component losses, saturation, non-linearity, harmonics, transients or a complete network.
Ideal transformer ratios
Calculate one ideal voltage or current term from the entered turns ratio.
Vp / Vs = Np / Ns; Ip / Is = Ns / Np.
- Symbols and basis
- V = voltage; I = current; N = turns; p = primary; s = secondary.
This ideal relationship excludes losses, regulation, vector group, taps, impedance, insulation, thermal limits and protection.
Motor speed and slip
Calculate synchronous speed, induction-motor slip, or rotor speed using a simplified motoring model.
ns = 120f / p; s = (ns − nr) / ns × 100%.
- Symbols and basis
- ns = synchronous speed; nr = rotor speed; f = frequency in hertz; p = even pole count; s = slip.
This does not predict torque, starting current, load response, motor condition, direction of rotation or an acceptance condition.
Need definitions, worked examples and safety boundaries? Read Electrical Engineering Fundamentals.