RC time constant calculator

tau = R times C is the time a capacitor takes to reach 63.2 percent of the supply, and it is a proportionality: two tau is 86.5 percent, three is 95 percent, five is 99.3. The same tau sets the filter cutoff at 1/(2 pi RC), where gain is 3 dB down and phase is 45 degrees. This is the ideal first-order model. It stops being true once electrolytic ESR, dielectric absorption, or DC-bias derating enter the picture, and real capacitors lose a lot of their marked value near their voltage limit.