Impedance Calculator (Basic)

Impedance calculator for R, X, and basic series RLC circuits

Electrical impedance is the “total opposition” a circuit presents to alternating current (AC). It combines resistance (the part that dissipates energy as heat) and reactance (the part that stores and releases energy in magnetic or electric fields). Reactance can be inductive (from inductors) or capacitive (from capacitors). Because reactance depends on frequency, impedance usually changes when the frequency changes.

This Impedance Calculator (Basic) is designed for the most common quick calculations: converting resistance and reactance into impedance magnitude and phase angle, and estimating series RLC impedance using frequency plus optional inductance and capacitance. It gives you more than one number, because impedance is a complex value. For practical work, the two most useful outputs are the magnitude |Z| in ohms (Ω) and the phase angle in degrees, which tells you how far current leads or lags voltage.

Use the “Resistance and reactance (R and X)” method when you already know the real part (R) and the imaginary part (X). This is common when you have measurements, datasheet values, or you have already calculated reactance elsewhere. Use the “Series RLC with frequency” method when you want the calculator to derive reactance from inductance, capacitance, and frequency. Inductance and capacitance are optional so you can still get a useful result even if you only know one of them, or if you want to treat one component as negligible.

Assumptions and how to use this calculator

• This calculator uses a simple series impedance model: Z = R + jX, where X is net reactance (XL − XC).
• Inductor reactance is calculated as XL = 2πfL, and capacitor reactance as XC = 1 ÷ (2πfC) when C is provided and greater than 0.
• If you leave L or C blank in the series RLC mode, it is treated as 0, meaning that component is ignored for the net reactance.
• Phase angle is computed as atan(X/R) in degrees. When R is 0, the phase is treated as +90° or −90° based on the sign of X, and 0° when both R and X are 0.
• Power factor is reported as cos(phase angle). This is a simplified indicator for series loads and is not a full power analysis for non-sinusoidal waveforms or complex networks.

Common questions

What is the difference between impedance and resistance?

Resistance is the “real” part of opposition to current and does not depend on frequency for ideal resistors. Impedance includes resistance plus reactance, and reactance changes with frequency. In AC circuits, impedance is the correct total value to use when calculating current from voltage.

Why can reactance be negative?

In the common sign convention, inductive reactance is positive and capacitive reactance is negative. A negative reactance means the circuit behaves more like a capacitor overall, which typically causes current to lead voltage. A positive reactance means it behaves more like an inductor, which typically causes current to lag voltage.

What does the phase angle tell me in practice?

The phase angle indicates the timing relationship between voltage and current for a sinusoidal AC signal. A positive angle suggests an inductive load (current lags), and a negative angle suggests a capacitive load (current leads). This directly affects power factor and can impact system efficiency, sizing, and power quality considerations.

Can I use this for parallel circuits or complex networks?

Not reliably. This calculator is intentionally basic and assumes a series model. Parallel circuits require converting to admittance or combining impedances using reciprocal formulas. If you have multiple branches, frequency-dependent losses, or multiple stages, you should use a network calculator or circuit simulation tool.

How can I improve accuracy if I only have rough values?

Start with the quick mode using estimated R and X to get a fast magnitude and phase. If you know the frequency and at least one of L or C, switch to the series RLC mode and add the missing component if you can. For higher accuracy, use measured values at the actual operating frequency and include realistic resistance for coils and capacitor ESR where possible.