RC Time Constant Calculator

The RC time constant (τ) determines how quickly a resistor-capacitor circuit charges, discharges, or filters signals.

Time constant:

τ = R × C

Cutoff frequency (for RC low-pass or high-pass filters):

f_c = 1 / (2π × R × C)

At the cutoff frequency, the signal is attenuated to -3 dB (70.7% of input).

RC Low-Pass Filter:

• Passes frequencies below f_c
• Blocks frequencies above f_c
• Used for smoothing, noise reduction

RC High-Pass Filter:

• Passes frequencies above f_c
• Blocks frequencies below f_c
• Used for AC coupling, removing DC offset

Rise time (10% to 90%):

t_rise ≈ 2.2 × τ

Common applications:

• Audio tone controls
• Power supply filtering
• Signal debouncing
• Sensor smoothing