🔌 Electrical calculators
Free online electrical calculators for electricians, electrical engineers and students. Convert kW to amps and kVA to kW, check cable voltage drop, size a capacitor bank for power factor correction, find transformer full-load and short-circuit current, size earth conductors and measure THD — with formulas, worked examples and reference tables on every page.
26 free calculators · no sign-up · works on mobile
Power & currentMotors & drivesTransformers & fault levelCables, earthing & power quality
Most popular electrical calculators
- Cable Voltage Drop CalculatorCalculate voltage drop in copper or aluminium cable for single-phase and three-phase circuits — and the minimum cable size.
- kVA to kW Converter (and kW to kVA)Convert kVA to kW and kW to kVA using power factor — for generators, UPS, transformers and DG set sizing.
- kW to Amps Calculator (Single-Phase, Three-Phase and DC)Convert kilowatts to amps for single-phase, three-phase and DC circuits using voltage and power factor — with charts for 230 V and 415 V.
- Power Factor Correction Calculator (Capacitor kVAr)Calculate the capacitor bank kVAr and capacitance needed to raise power factor from its present value to a target — with current reduction.
- Three-Phase Motor Power & Current CalculatorCalculate input power, output power and full-load current of a three-phase motor from voltage, power factor and efficiency.
Power & current
- kW to Amps Calculator (Single-Phase, Three-Phase and DC)Convert kilowatts to amps for single-phase, three-phase and DC circuits using voltage and power factor — with charts for 230 V and 415 V.
- Amps to Watts Calculator (and Watts to Amps)Convert amps to watts for DC, single-phase and three-phase circuits — with charts for 12 V, 120 V and 230 V.
- kVA to kW Converter (and kW to kVA)Convert kVA to kW and kW to kVA using power factor — for generators, UPS, transformers and DG set sizing.
- Line and Phase Voltage Calculator (Star and Delta)Convert between line and phase voltage and current for star (wye) and delta connections — with three-phase power from either.
- Power Factor Correction Calculator (Capacitor kVAr)Calculate the capacitor bank kVAr and capacitance needed to raise power factor from its present value to a target — with current reduction.
- UPS Size Calculator (kVA)Calculate the UPS kVA rating needed for your load from watts, power factor and a growth margin — for homes, offices, servers and control panels.
- Generator Size Calculator (DG Set kVA)Calculate the diesel generator (DG set) kVA rating needed for your connected load, power factor, future margin and largest motor start.
Motors & drives
- Three-Phase Motor Power & Current CalculatorCalculate input power, output power and full-load current of a three-phase motor from voltage, power factor and efficiency.
- Motor Starting Current Calculator (DOL, Star-Delta, Soft Starter)Estimate the starting (inrush) current of an induction motor for DOL, star-delta, autotransformer and soft-starter starting from full-load current.
- Induction Motor Slip and Synchronous Speed CalculatorCalculate synchronous speed, slip and rotor frequency of an induction motor from supply frequency, number of poles and rated speed.
- Voltage Unbalance Calculator (NEMA Method)Calculate percentage voltage unbalance from three line voltages, plus the motor derating and extra temperature rise it causes.
- VFD Braking Resistor CalculatorCalculate the maximum braking resistor value and average power rating for a VFD braking chopper from DC bus voltage, braking power and duty cycle.
Transformers & fault level
- Transformer Size Calculator (kVA Rating from Load)Calculate the transformer kVA rating needed for your connected load from kW, power factor, diversity factor and future growth — and pick the next standard size.
- Transformer Current Calculator (Full-Load Amps)Calculate primary and secondary full-load current of single-phase and three-phase transformers from kVA and voltages.
- Transformer Short-Circuit Current CalculatorEstimate the maximum fault current on a transformer secondary from kVA, voltage and percentage impedance (infinite-bus method).
- Transformer Turns Ratio CalculatorCalculate transformer secondary voltage, turns ratio and primary or secondary current from the number of turns or voltages.
- Transformer Efficiency Calculator (Iron and Copper Losses)Calculate transformer efficiency at any load and power factor from no-load (core) and full-load (copper) losses — plus the load for maximum efficiency.
- Per-Unit System Calculator (Base Impedance and Base Change)Calculate base impedance, base current and per-unit impedance for power system studies — and convert per-unit values to a new base.
- CT Burden Calculator (VA)Calculate current transformer (CT) burden in VA from secondary current, lead length, cable size and relay or meter burden — and check it against the CT rating.
Cables, earthing & power quality
- Cable Voltage Drop CalculatorCalculate voltage drop in copper or aluminium cable for single-phase and three-phase circuits — and the minimum cable size.
- Wire Resistance Calculator (Copper and Aluminium)Calculate the resistance of a copper or aluminium wire or cable from length, cross-section and temperature — plus resistance per km.
- Earth Fault Loop Impedance Calculator (Zs)Calculate prospective earth fault current from loop impedance Zs, or the maximum Zs for an MCB to trip within 0.4 s — for TN systems.
- Earth Conductor Size Calculator (Adiabatic Equation)Calculate the minimum protective earth conductor size from fault current and disconnection time with the adiabatic equation S = I√t / k (IEC 60364-5-54).
- Earthing Resistance Calculator (Earth Rod)Calculate the earth resistance of a vertical earth rod or pipe electrode from soil resistivity, length and diameter — and how many rods you need.
- THD Calculator (Total Harmonic Distortion)Calculate total harmonic distortion (THD) of voltage or current from the fundamental and harmonic magnitudes, with IEEE 519 limits.
- Star-Delta (Y-Δ) Transformation CalculatorConvert delta (Δ) resistances or impedances to an equivalent star (Y), and star to delta — for circuit analysis and network simplification.
For LV and MV power systems
The calculators cover single-phase, three-phase and DC circuits at common Indian, European and North American voltages (230/415 V, 400 V, 120/208/480 V and 11 kV). Formulas follow IEC 60364, IEC 60076, IEEE 519 and NEMA MG 1 where relevant, and each page explains the assumptions.
From quick checks to design
Use them for quick site checks — will this cable drop too much voltage, how many amps will this motor draw — or as a starting point for design. For final designs, always confirm against manufacturer data and your local wiring regulations.
Frequently asked questions
How do I convert kW to amps for a three-phase motor?
I = P ÷ (√3 × V × PF × efficiency). Use the kW to amps or three-phase motor power calculator, which apply this formula for you.
Do these calculators work for 50 Hz and 60 Hz systems?
Yes. Where frequency matters — such as power factor correction or motor speed — you can enter 50 or 60 Hz.
Are the results suitable for final design?
They are accurate for the formulas shown, but final designs must also consider installation conditions, derating and local regulations.
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