RC Time Constant Calculator
Compute τ = R × C for a resistor-capacitor pair. Default 1000 Ω and 10 µF gives τ = 0.01 s. The page also shows 5τ, about 99.3% of full charge on an ideal step. Informational only.
Rated 4.7 out of 5 based on 388 reviews
How to find the RC time constant
- Enter resistance in ohms. Default is 1000 Ω.
- Enter capacitance and pick the unit. Default is 10 µF.
- Read τ in seconds and 5τ as a rough full-charge time constant.
- This is an ideal exponential model. Nothing is uploaded.
RC time constant
τ = R × C
| Tau | Seconds to reach ~63.2% of final voltage on a step |
|---|---|
| Five tau | About 99.3% of final value |
| Resistance | Ohms in series with the capacitor path |
| Capacitance | Farads after unit conversion |
| Default | 1 kΩ × 10 µF = 0.01 s |
| Approval | Informational. Not a timing sign-off. |
What tau means
On a simple RC charge, voltage approaches the supply exponentially with time constant τ = R × C. After one τ the capacitor is at about 63.2% of the final value. After 5τ it is within about 0.7% of final on the ideal curve.
Unit conversion
Capacitance accepts F, mF, µF, nF, or pF. Resistance stays in ohms. The engine converts to base SI before multiplying.
Charge and energy
Charge Q = C × V is on capacitance to charge. Plate geometry C is on parallel plate capacitance.
Limits
Single RC, ideal components, no ESR or leakage modeled.
The formula runs in this tab. CZNull does not receive the numbers.
Informational only. Not wiring, code, or manufacturer approval. See the disclaimer.