Electrical Circuit Calculator
Electrical and electronic calculations from basic DC to AC and amplifier circuits, with formulas and frequency-response charts.
Ohm's Law and Power
Enter exactly two known positive values among voltage, current, resistance and power. The other two are calculated.
Series and Parallel Resistors
Enter two or more resistance values to calculate the equivalent resistance for both series and parallel connections.
Series and Parallel Capacitors
Enter two or more capacitance values. Parallel capacitances add directly, while series capacitances use the reciprocal sum.
RC Time Constant
Calculate the time constant τ from resistance and capacitance, with useful charging and discharging time landmarks.
RC/CR Cutoff Frequency
Calculate the −3 dB cutoff frequency of a first-order RC low-pass or CR high-pass circuit.
Voltage Divider
For an unloaded resistive divider, calculate output voltage, division ratio, circuit current and power in each resistor.
A connected load changes the output voltage because it appears in parallel with R2. This calculation assumes an ideal unloaded divider.
LED Current-Limiting Resistor
Calculate resistance from series LED forward voltage and target current, then show a safer upward-rounded E12 value and power-rating guide.
Vf changes with current, temperature and device variation. Check the LED datasheet, resistor tolerance and ratings, and allow adequate design margin in a real circuit.
AC Impedance
Calculate complex impedance for a series or parallel RLC circuit, with magnitude and phase from 1/100 to 100 times the entered frequency. Magnitude uses log scales on both axes; phase uses a logarithmic frequency axis.
RLC Resonance
Calculate resonant frequency, Q factor, bandwidth and half-power frequencies for an ideal series or parallel RLC circuit.
The parallel model places R, L and C directly in parallel. Series resistance and other losses in real components are not included.
Decibels and Ratios
Convert voltage or power ratios to and from dB. Voltage ratios use 20 log₁₀, while power ratios use 10 log₁₀.
Basic Op-Amp Circuits
Calculate gain and output voltage for ideal inverting, non-inverting, two-input summing and differential amplifiers.
This is an ideal op-amp calculation. It does not account for supply-rail saturation, input/output range, gain bandwidth, slew rate or offset voltage.