τ = R · C. Enter R and C to see the time constant, settling times at 1τ through 5τ, and the cutoff frequency of an RC filter — all visualized live.
The time constant τ = R · C tells you how fast a capacitor charges through a resistor. After one τ, the capacitor reaches 63.2% of the supply voltage. After 5τ, it's at ~99.3% — engineers usually call this "fully charged."
The same constant determines the cutoff frequency of a single-pole RC filter: fc = 1 / (2π·R·C). Below fc, signals pass; above fc, they're attenuated.
Tip: for debouncing a button, target τ between 5–20 ms. For audio low-pass filters, fc determines the rolloff point — 20 kHz for full audio range, much lower for anti-aliasing.