Tool · Circuit fundamentals
RC Time Constant Calculator
Calculate τ = RC, see how a capacitor charges and discharges, and connect the curve to real timing and filtering behavior.
Calculate
Inputs
Calculate
Results
Approx. 99.3% settling time: 5τ = 5 s
Visualize
Watch the exponential response.
The curves use time constants on the horizontal axis, so their shape is comparable across different R and C values.
Charging starts quickly and then approaches Vs more slowly. Discharging follows the same exponential shape in the opposite direction, approaching 0 V without reaching it in finite time.
Understand
How the RC calculation works
Time constant
τ = R × Cτ = 10 kΩ × 100 µF = 1 s
Charging voltage
Vc(t) = Vs × (1 − e−t/τ)At one time constant, the capacitor has completed about 63.2% of the change toward its final voltage.
What changes what?
Increase R → charging and discharging become slower → τ increases.
Increase C → more charge storage is needed for the same voltage change → τ increases.
Decrease either R or C → τ decreases → the circuit responds faster.
Apply
Engineering interpretation
RC networks can create timing or delay behavior, but a simple RC is not a precision digital timer.
As a low-pass filter, an RC network can smooth faster voltage changes while allowing slower changes to pass more readily.
RC behavior is useful for switch debouncing and reset or power-on delay circuits when the timing tolerance is understood.
Sensor smoothing can reduce rapid noise, but resistor/capacitor tolerance, leakage, source and load impedance, and capacitor non-ideal behavior affect the result.
At 5τ, an ideal charging capacitor is about 99.3% of its final value—not mathematically 100%. The exponential response only approaches the final value asymptotically.