RC Time Constant Calculator — τ = R · C Charge and Discharge

Free RC time constant calculator for designing filters, timers, debounce circuits and any resistor-capacitor pair. The time constant is τ = R · C: a 10 kΩ resistor with a 100 µF capacitor gives τ = 1 second, while 10 kΩ with 100 nF gives 1 ms. Enter resistance in Ω, kΩ or MΩ and capacitance in F, µF, nF or pF, and the tool computes τ and shows how the capacitor voltage evolves over time. For charging it uses V(t) = V0·(1 − e^(−t/τ)), reaching 63.2% of the supply at one τ and about 99.3% at five τ, the point engineers treat as fully charged. For discharging it uses V(t) = V0·e^(−t/τ), falling to 36.8% at one τ. A voltage curve, a table at 0τ through 5τ, one-click copy and a shareable URL that reproduces your exact circuit all run in your browser. 100% client-side, no upload.