Electrical calculators
Electrical calculators for wiring, panels, and low-voltage circuits. Results are estimates: verify against the current NEC and your local code.
- Battery Runtime CalculatorRuntime in hours equals battery volts × amp-hours × usable fraction × efficiency ÷ load watts.Inputs: Battery voltage, Capacity, Usable share of the capacity
- Conduit Fill CalculatorAdd up the cross-sectional area of every conductor and pick the smallest conduit whose allowed fill (53%, 31%, or 40% by wire count) is at least that big.Inputs: Conduit type, Installation, Conductor size and type, group 1
- Conduit Offset Bend CalculatorThe distance between the two bends is the offset height divided by the sine of the bend angle, and the conduit shrinks by the offset times tan(half the angle).Inputs: Offset height, Bend angle
- Electrical Box Fill CalculatorEach conductor, device, clamp set, and ground set takes a volume allowance from NEC Table 314.16(B); add them up and compare to the volume stamped on the box.Inputs: Conductor size, Conductors that start outside the box and end in it, Devices
- Generator Sizing CalculatorAdd up the running watts of everything you will power at once, then add the highest starting watts of any one motor; that total is the surge rating you need.Inputs: Resistive and electronic loads, All motor loads, running watts total, Starting watts of the biggest motor
- Inductive and Capacitive Reactance CalculatorInductive reactance is X_L = 2πfL and capacitive reactance is X_C = 1 ÷ (2πfC), both in ohms; they cancel at the resonant frequency.Inputs: Frequency, Inductance, Inductance unit
- kVA, kW, and Amps CalculatorSingle-phase kVA = volts × amps ÷ 1,000; three-phase kVA = √3 × volts × amps ÷ 1,000; kW = kVA × power factor.Inputs: I know, System, Line voltage
- Motor Full-Load Amps and Wire Size CalculatorThe NEC lists a full-load current for each motor horsepower and voltage, and the branch-circuit conductors are sized at 125% of that value.Inputs: Motor type and voltage, Horsepower, Conductor
- Ohm's Law CalculatorOhm's law says voltage = current × resistance, and power = voltage × current; give the calculator any two and it finds the other two.Inputs: I know, Voltage, Current
- Power Factor Correction CalculatorRequired capacitor kVAR = real power (kW) × (tan of the present power-factor angle − tan of the target angle).Inputs: Real power, Present power factor, Target power factor
- RC Time Constant CalculatorThe RC time constant τ equals resistance in ohms times capacitance in farads, and a capacitor reaches about 63% of full charge in one τ.Inputs: Resistance, Resistance unit, Capacitance
- Resistors in Series and Parallel CalculatorSeries resistances add, parallel resistances combine as 1 ÷ (1/R₁ + 1/R₂ + …), and a divider output is Vin × R₂ ÷ (R₁ + R₂).Inputs: Resistor 1, Resistor 2, Third resistor
- RL Time Constant CalculatorThe RL time constant τ equals inductance in henries divided by resistance in ohms, and inductor current reaches about 63% of its final value in one τ.Inputs: Inductance, Inductance unit, Total series resistance
- Solar Panel and Battery Bank Sizing CalculatorArray size = daily energy use ÷ (peak sun hours × (1 − system losses)), and battery capacity = daily use × days of autonomy ÷ depth of discharge.Inputs: Daily energy use, Peak sun hours per day, System losses
- Voltage Drop CalculatorVoltage drop = 2 × K × current × one-way length ÷ circular mils for single-phase (K = 12.9 for copper, 21.2 for aluminum).Inputs: Source voltage, Load current, One-way length
- Wire Size by Ampacity CalculatorDivide the load (times 1.25 if continuous) by any derating factor, then pick the smallest wire whose NEC 310.16 ampacity in the right temperature column is at least that current.Inputs: Load current, Load type, Conductor