How fast does a capacitor charge through a resistor?
Vc(t) = Vf + (V0 − Vf) · e^(−t/RC). After one time constant τ = RC the capacitor has covered 63.2 % of the step, 95 % after 3τ and 99.3 % after 5τ.
Vc(t) = Vf + (V0 − Vf) · e^(−t/RC)
RC time constant calculator
Capacitor voltage over time, time to reach a threshold, or the capacitor you need for a given delay, with the nearest standard value.
RC circuit
Accepted: 100n · 4u7 · 2.2µF · 470p · 1m (mF)
Times: 250ns · 47us · 1.5ms · 2s · 3min (no unit = seconds)
Vc(t)
time t
target voltage
final voltage
Time-constant table
Capacitor voltage and current at common multiples of τ = RC.
| Time constants | Time | Vc | Step completed | Current |
|---|
Standard capacitor for the desired delay
Frequently asked questions
How long does it take to reach a given voltage?
t = −RC · ln((Vt − Vf) / (V0 − Vf)). The target must lie between the start and final voltages; the final voltage itself is only reached asymptotically.
Which capacitor values are standard?
Capacitors are usually sold in E6 or E12 values (1, 1.5, 2.2, 3.3, 4.7, 6.8…). The calculator gives the exact value for your delay and the nearest E6, E12 and E24 values.