RC Time Constant Calculator

About this calculator

This calculator finds the RC time constant (τ = R × C) of a resistor-capacitor circuit, along with how long the capacitor takes to charge or discharge to common thresholds like 63%, 95%, or 99% of full voltage. One time constant is always the time it takes to cover 63.2% of the remaining change.

Electronics hobbyists and engineering students use it to design timing circuits, debounce switches, and set filter cutoff frequencies, since the RC constant directly determines how fast a circuit responds to a voltage change. Enter the resistance and capacitance to get the time constant in seconds.