RLC Resonant Frequency Calculator

This calculator finds the resonant frequency of an RLC circuit from the inductance (L) and capacitance (C). It also calculates the angular frequency in radians per second, and if you enter the resistance (R) as well, it returns the Q factor (quality factor) which tells you how sharply the circuit resonates. An RLC circuit contains a resistor, an inductor and a capacitor. At the resonant frequency, the inductive and capacitive reactances are equal and opposite, leaving only the resistance to limit the current. In a series RLC circuit this means impedance is at its lowest and current is at its highest. In a parallel RLC circuit the opposite is true: impedance is highest and current is lowest at resonance. The resonant frequency is determined solely by L and C, not by R. The formula is f0 = 1 / (2 x pi x square root of (L x C)), where L is in henries and C is in farads. The angular frequency is omega0 = 2 x pi x f0 = 1 / square root of (L x C). The Q factor for a series circuit is Q = (1/R) x square root of (L/C); a higher Q means a sharper, more selective resonance and less energy lost per cycle. RLC circuits are used in radio tuners to select a specific frequency, in notch and bandpass filters, in oscillator circuits, and in switched-mode power supply design. Enter L in millihenries and C in microfarads for typical audio and power circuits, or adjust the units in the fields below.

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L and C inputs are in mH and uF. Q factor requires resistance. Higher Q = sharper, more selective resonance.