RC Filter Cutoff Calculator

About this calculator

An RC filter's cutoff frequency — the −3 dB point where the output power drops to half its passband value — is given by f_c = 1 / (2π·R·C), determined entirely by the resistor's resistance R and capacitor's capacitance C in the circuit. In a low-pass configuration, frequencies below f_c pass through largely unattenuated while higher frequencies are increasingly suppressed; in a high-pass configuration, the roles reverse.

Electronics engineers and hobbyists use this formula constantly when designing audio crossovers to split frequencies between speaker drivers, building signal-conditioning circuits to filter noise from sensor readings, and designing timing and coupling circuits. Electronics and electrical engineering students learn it as one of the first practical filter-design formulas, since it directly connects a circuit's component values to its frequency-domain behavior.