Calculators

Electrical calculators with the working shown

Twenty-three tools for circuit laws, cables, batteries, AC power, motors, automotive charging and EV charging. Every result shows the formula, the substituted values, the unit and the assumptions — never a fabricated answer.

Circuit laws Cables & batteries Automotive & EV

Laws

1 calculator in this group.

Ohm's Law Calculator

Solve V = I × R for voltage, current or resistance and check power.

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Power

5 calculators in this group.

Electrical Power Calculator

Calculate DC power from voltage, current or resistance using P = VI, P = I²R and P = V²/R.

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Electrical Energy Calculator

Convert power and time into watt-hours, kilowatt-hours and energy cost.

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AC Power Calculator

Real, reactive and apparent power from RMS voltage, current and power factor.

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Three-Phase Power Calculator

Real, reactive and apparent power for a balanced three-phase load.

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Power Factor Calculator

Calculate power factor, phase angle and the capacitance needed for correction.

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Circuits

4 calculators in this group.

Series Resistance Calculator

Total resistance of resistors connected in series, plus current and power for a supply voltage.

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Parallel Resistance Calculator

Equivalent resistance of parallel branches and the current in each branch.

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Voltage Divider Calculator

Output voltage of a two-resistor divider and the current through it.

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Current Divider Calculator

Split a total current between two parallel resistors.

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Cables

3 calculators in this group.

Voltage Drop Calculator

Estimate voltage drop and percentage loss in a cable run.

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Cable Resistance Calculator

Resistance of a conductor from resistivity, length and cross-sectional area.

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Cable Sizing Calculator

Educational cable-size estimate from current and voltage-drop limits.

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Reference

1 calculator in this group.

Electrical Unit Converter

Convert voltage, current, resistance and power between SI prefixes.

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Batteries

2 calculators in this group.

Battery Energy Calculator

Convert amp-hours and voltage to watt-hours and kilowatt-hours.

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Battery Runtime Calculator

Estimate runtime from battery capacity, load current and depth of discharge.

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Components

3 calculators in this group.

LED Resistor Calculator

Choose a series resistor for an LED and check its power dissipation.

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Capacitor Calculator

Charge, stored energy and time constant for a capacitor.

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RC Time Constant Calculator

Time constant and charge/discharge milestones for an RC circuit.

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Machines

1 calculator in this group.

Motor Efficiency Calculator

Efficiency, losses and input power for an electric motor.

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Automotive

2 calculators in this group.

Automotive Fuse Calculator

Estimate a fuse rating from continuous load current and a safety margin.

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Alternator Output Calculator

Sum vehicle electrical loads and estimate the alternator headroom at idle.

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Ev

1 calculator in this group.

EV Charging Time Calculator

Estimate charging time from battery capacity, state of charge and charger power.

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Engineering disclaimer. These calculators are educational. Cable sizing, fuse selection, alternator load balance and power-factor correction are simplified models; a real installation needs verification against the applicable standard, the equipment datasheet and a qualified professional.