Enter a positive resistance value.
Enter a positive capacitance value.
RC Time Constant Result
Quick Examples
RC Charging and Discharging
A capacitor changes exponentially during charging and discharging. The table below shows the capacitor voltage as a percentage of the final or initial voltage.
| Time | Charging | Discharging | Time Value |
|---|
RC Charging and Discharging Curve
Visualize how the capacitor voltage changes over time.
How the RC Time Constant Works
The RC time constant is an important parameter in electronic circuits that contain both a resistor and a capacitor.
What Is an RC Time Constant?
The RC time constant, represented by τ (tau), describes how quickly a capacitor charges or discharges through a resistor.
It is calculated using:
τ = R × C
- τ = Time Constant in seconds
- R = Resistance in ohms
- C = Capacitance in farads
Capacitor Charging
During charging, capacitor voltage follows an exponential curve.
The ideal charging equation is:
V(t) = V × (1 − e−t/RC)
- After 1τ: approximately 63.2%
- After 2τ: approximately 86.5%
- After 3τ: approximately 95.0%
- After 5τ: approximately 99.3%
Capacitor Discharging
During discharging, capacitor voltage decreases exponentially.
The ideal discharge equation is:
V(t) = V0 × e−t/RC
- After 1τ: approximately 36.8%
- After 2τ: approximately 13.5%
- After 3τ: approximately 5.0%
- After 5τ: approximately 0.7%
What Affects the Time Constant?
The RC time constant increases when either resistance or capacitance increases.
- Higher resistance → Longer time constant
- Higher capacitance → Longer time constant
- Lower resistance → Faster charging/discharging
- Lower capacitance → Faster charging/discharging
Engineering Note: Ideal RC Calculation
This calculator uses ideal RC equations. In real circuits, the actual charging and discharging behavior may also be affected by capacitor tolerance, leakage current, equivalent series resistance (ESR), circuit loading, switching devices and other parasitic components.
Common RC Time Constant Applications
RC circuits are widely used in electronic and electrical systems.
Timing Circuits
RC circuits can create predictable delays and timing intervals.
Signal Filtering
Resistors and capacitors are commonly used in low-pass and high-pass filters.
Signal Conditioning
RC networks can smooth, delay or shape electrical signals.
EMI and Noise Suppression
Capacitors and RC networks may be used to reduce unwanted high-frequency noise and interference.