RC Filter Cutoff Calculator Formula

Understand the math behind the rc filter cutoff calculator. Each variable explained with a worked example.

Use the RC Filter Cutoff Calculator

Formulas Used

Cutoff Frequency

cutoff_hz = 1 / (2 * pi * resistance * c_f)

Time Constant (RC)

time_constant = resistance * c_f * 1000

Variables

VariableDescriptionDefault
resistanceResistance(Ω)1000
capacitance_nfCapacitance(nF)100
c_fDerived value= capacitance_nf / 1000000000calculated

How It Works

RC Filter Cutoff

f_c = 1 / (2 x pi x R x C)

At the cutoff frequency, output is -3 dB (70.7%) of the input. The time constant tau = RC.

Worked Example

R = 1k, C = 100 nF.

resistance = 1000capacitance_nf = 100
  1. 01C = 100 nF = 1e-7 F
  2. 02f_c = 1 / (2pi x 1000 x 1e-7) = 1591.5 Hz
  3. 03tau = 1000 x 1e-7 = 0.1 ms

Ready to run the numbers?

Open RC Filter Cutoff Calculator