Calculators
Syllabus-aligned circuit math with step-by-step working — live, offline, copy-friendly.
Ohm's Law — V = I × R
Enter any two of voltage, current or resistance. Leave the third blank to solve for it. Power (P = V × I) is computed automatically.
Enter at least two values to compute the third.
Common trap: Current is not used up as it flows around a circuit — the same current that leaves the battery returns to it. What a resistor drops is voltage, and what the circuit converts is energy.
Every calculator, explained
Each tool has its own page with the formula it uses, a worked example and the laws behind it.
Basics
Ohm's Law Calculator & Power FormulaV = I × RElectrical Power CalculatorP = V × I = I² × R = V² / RResistivity Calculator (R = ρL/A)R = ρ × L / AJoule Heating CalculatorH = I² × R × tLED Resistor Calculator & FormulaR = (V_supply − V_forward) / I_forwardVoltage Divider Calculator & FormulaV_out = V_in × R₂ / (R₁ + R₂)Reverse Voltage Divider CalculatorR₂ / (R₁ + R₂) = V_out / V_inSeries and Parallel Resistance CalculatorSeries: R = R₁ + R₂ + …RC Time Constant Calculatorτ = R × C
Networks
AC & Power
Capacitive and Inductive Reactance CalculatorX_C = 1 / (2πfC)LC Resonance Calculatorf₀ = 1 / (2π√(LC))RLC Impedance Calculator & FormulaZ = √(R² + (X_L − X_C)²)Power Triangle CalculatorS² = P² + Q²3 Phase Power Calculator & FormulaS = √3 × V_L × I_LTransformer Turns Ratio CalculatorN_p / N_s = V_p / V_s = I_s / I_pPower Factor Correction CalculatorQ_c = P × (tan φ₁ − tan φ₂), where φ = arccos(pf)RMS, Average and Form Factor CalculatorSine wave: V_rms = V_peak / √2
Machines
EM & Fields
Electronics
555 Timer CalculatorAstable: t_high = 0.693(R₁+R₂)C, t_low = 0.693 R₂C, f = 1/(t_high+t_low)Op-Amp Gain CalculatorInverting: A_v = −R_f / R_inBJT Base Resistor CalculatorI_b(min) = I_c / h_FEZener Diode Regulator CalculatorR_s = (V_in − V_z) / (I_load + I_z(min))Rectifier CalculatorHalf-wave: V_dc = V_pk/πCapacitor and Inductor Stored Energy CalculatorE = ½ × C × V² (capacitor)
Everyday
Energy and Electricity Bill CalculatorUnits (kWh) = (Watts / 1000) × hoursResistor Colour Code CalculatorValue = (digit bands) × 10^multiplier, ± tolerance bandCapacitor Code CalculatorValue in pF = (first two digits) × 10^(third digit)SMD Resistor Code Calculator3/4-digit: value = (leading digits) × 10^(last digit)Component Substitute Checkerat-least: candidate ≥ originalBattery Life CalculatorRuntime (h) = (Capacity in mAh / Load in mA) × derating factorWire Voltage Drop CalculatorR_cable = ρ × (2 × L) / AIllumination Calculator (Lux)E = I / d²
Installation & sizing
Motor Full Load Current CalculatorI = kW × 1000 / (√3 × V × η × cos φ) [three phase]HP to kW Converter & FormulakW = hp × 0.7355 (metric)kVA to Amps Calculator & FormulaI = kVA × 1000 / (√3 × V) [three phase]kVA to kW Calculator & Conversion FormulakW = kVA × pfCable Size CalculatorI_z = I_table × k_ambient × k_groupingMCB & RCCB Selection CalculatorI_b ≤ I_n ≤ I_zEarthing Conductor Size CalculatorS = √(I² t) / kElectricity Bill Calculator (Slabs)Bill = Σ(units in each slab × that slab's rate) + fixed charge × sanctioned kW + duty
Protection & testing
Short Circuit Fault Current CalculatorI_sc = I_fl × 100 / %ZOverload Relay & Contactor CalculatorDOL: setting = I_flBusbar Size Calculator & Current Rating ChartI = J × AEarth Pit Resistance Calculator (IS 3043)Rod: R = ρ/(2πL) × [ln(8L/d) − 1]Insulation Resistance (Megger) CalculatorR₄₀ = R_measured × 2^((T − 40)/10)