RC Time Constant Calculator
Charge time and cutoff frequency.
Enter your values
Enter the resistance in kΩ.
Enter the capacitance in µF.
Enter the supply voltage in V.
Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.
- Time constant
- 1 s
- Time to 99% charge
- 5 s
- Voltage after 1τ
- 7.58 V
- Cutoff frequency
- 0.16 Hz
Quick answer
One RC time constant charges a capacitor to 63% of the supply voltage.
τ = R × C
At a glance
| What it does | Charge time and cutoff frequency. |
|---|---|
| Category | Engineering |
| Inputs needed | Resistance, Capacitance, Supply voltage |
| Main output | Time constant |
| Formula | τ = R × C |
| Cost | Free — no sign-up, no download |
How to use the RC Time Constant Calculator
- 1Enter resistance in kilohms.
- 2Enter capacitance in microfarads.
- 3Enter supply voltage.
Inputs explained
- Resistance(kΩ)
- Enter the resistance in kΩ.
- Capacitance(µF)
- Enter the capacitance in µF.
- Supply voltage(V)
- Enter the supply voltage in V.
Worked example
Using the values the calculator loads with:
Inputs
- Resistance10 kΩ
- Capacitance100 µF
- Supply voltage12 V
Results
- Time constant1 s
- Time to 99% charge5 s
- Voltage after 1τ7.58 V
- Cutoff frequency0.16 Hz
Frequently asked questions
Why five time constants?
After 5τ the capacitor is over 99% charged, treated as fully charged.
Is discharge the same?
Yes — it falls to 37% after one time constant.
What do I need to enter into the RC Time Constant Calculator?
Just 3 values: resistance, capacitance, supply voltage. Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.
How does the RC Time Constant Calculator work out the answer?
One RC time constant charges a capacitor to 63% of the supply voltage. It applies the formula τ = R × C and shows the working so you can check each step by hand.
Is the RC Time Constant Calculator free, and do I need an account?
It is completely free with no sign-up, no download and no usage limit. Everything is calculated in your browser, so the numbers you type never leave your device.
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.