Time Constant Calculator
The Time Constant (τ) represents the speed at which a circuit responds to a change in voltage. It is the time required to charge a capacitor (or energize an inductor) to 63.2% of its maximum capacity.
This tool supports both RC (Resistor-Capacitor) and RL (Resistor-Inductor) circuits. It generates a Precision Charge Curve to help you visualize the transient response.
Circuit Parameters
ms
Instantaneous Voltage
ms
Charge %:
— %
Dynamic Charge Curve
Live GraphFull Charge (5τ)
—
Cutoff Freq (fc)
—
Formulas
RC Time Constant
τ = R × C
Resistor (Ohms) × Capacitor (Farads)RL Time Constant
τ = L / R
Inductor (Henries) / Resistor (Ohms)5-Tau (Full Charge)
tfull ≈ 5 × τ
Time to reach 99.3% charge.Cutoff Frequency
fc = 1 / 2πτ
The -3dB point for filters.How to Use
Calculate circuit timing in 3 steps.
1
Select Circuit Type
Toggle between RC (Capacitor) and RL (Inductor) using the buttons at the top.
2
Enter Values
Input the Resistance and Capacitance/Inductance. Use the dropdowns to select units (e.g., µF, kΩ).
3
View Results
The Time Constant (τ) is calculated instantly. The tool also provides the time to full charge (5τ) and the cutoff frequency.