Electrical Calculators

Practical calculators for electricians, electrical engineers and serious DIYers. Wire sizing follows NEC conductor tables; every result shows the formula, the assumptions and the limitations of the model.

• Voltage Drop CalculatorCalculate voltage drop, % drop, end-of-line voltage and power lost for copper circuits. Single and three phase, AWG and metric, with NEC-based conductor data.
• Wire Size CalculatorFind the minimum copper wire size for your load current. NEC Table 310.16 ampacity at 75 °C, AWG and metric cross-sections, with margin over load and code notes.
• Ohm's Law CalculatorSolve any Ohm's law variable: leave one of voltage, current or resistance blank and get it, plus power in watts. Clean, fast and with a worked explanation.
• kVA to Amps CalculatorConvert kVA, kW or horsepower to amps for single and three-phase circuits. Includes kW↔kVA power factor conversion and the exact formulas used.
• Power Factor Correction CalculatorCalculate the capacitor kVAR needed to correct power factor from current to target. Shows apparent power freed, current reduction and the tan φ method.
• Motor Current CalculatorEstimate single or three-phase motor full-load current from hp, voltage, efficiency and power factor. Includes code notes on NEC 430 tables and 125% sizing.
• Wire Resistance CalculatorCalculate wire resistance from AWG size, length and material. Copper and aluminum, per 1000 ft and per meter, based on NEC Chapter 9 Table 8 data.
• Electricity Cost CalculatorCalculate what any appliance costs to run: kWh per day, month and year plus cost at your electricity rate. Multiplies for multiple identical devices.
• Transformer Sizing CalculatorSize a single-phase transformer from load kW and power factor, with design margin and primary/secondary currents. Standard kVA ratings listed.
• Three-Phase Power CalculatorCalculate three-phase real, apparent and reactive power from line voltage, current and power factor. The complete power triangle in one step.
• Voltage Divider CalculatorCalculate the output voltage of a two-resistor divider, with divider current and per-resistor dissipation. Includes loading warnings for real circuits.
• Resistor Color Code CalculatorDecode 4-band resistor values from band colors: resistance, tolerance and the acceptable range. Standard EIA color code with all twelve colors.
• LED Resistor CalculatorCalculate the current-limiting resistor for one or more LEDs, series or parallel, with power dissipation and nearest standard E12 values.
• EV Charging Time CalculatorCalculate EV charging time from battery size and charger power, including charge window, efficiency losses, range added and electricity cost.
• Generator Size CalculatorSize a backup generator from running watts and motor surge requirements. Includes the 25% continuous margin and motor starting guidance.
• Wire Derating CalculatorApply NEC 310.15 derating: temperature correction factors and conductor fill adjustments. Shows the effective ampacity after both reductions.
• Breaker Size CalculatorFind the correct breaker size for a load, including the 125% continuous-load rule and standard breaker ratings from 15 to 400 A.
• Cable Reactance CalculatorCalculate AC cable impedance including reactance for large conductors, where NEC Table 9 values matter. More accurate voltage drop for big wire runs.