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RC time constant calculator

How fast a capacitor charges through a resistor, the RC filter’s cutoff frequency, and the charge reached after any time.

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Time constant τ 1 s

How it works

τ = R × C · fc = 1 ÷ (2π R C)

In one time constant τ = R × C a charging capacitor reaches 63.2% of the supply voltage; after 5τ it’s above 99% and is treated as full. Discharging follows the same curve downward. The same R and C as a filter pass frequencies below fc = 1 ÷ (2πRC) and cut those above (low-pass), or the reverse (high-pass).

  1. τ = R × C 10,000 Ω × 0.0001 F = 1 s
  2. fc = 1 ÷ (2π τ) 1 ÷ (2π × 1) = 0.1592 Hz

Printed from rocketcalc.io/tech/rc-time-constant