RC Time Constant Calculator
Calculate the RC time constant τ for any resistor–capacitor network. Provide component values to learn how long it takes a capacitor to charge to about 63% of the supply voltage—critical for timing circuits, filters, and sensor conditioning.
Ideal RC circuit assumption; real components may vary.
Examples
- 1,000 Ω with 0.001 F capacitor ⇒ 1.0 second time constant
- 47 kΩ with 10 µF capacitor ⇒ 0.47 second time constant
- 220 Ω with 470 µF capacitor ⇒ 0.1034 second time constant
FAQ
What is the time constant?
It represents how quickly voltage across a capacitor rises or falls, reaching about 63% change after one τ.
Can I use kilo-ohms and microfarads?
Yes—just convert kΩ to Ω and µF to F before entering the values.
Does this account for inductance?
No, it applies only to RC circuits.
Why is τ important?
It dictates timing delays, filter roll-offs, and the response speed of sensing circuits.
How do I convert the result to milliseconds?
Multiply the seconds output by 1,000 to get milliseconds, or by 1,000,000 for microseconds.
Additional Information
- Time constant τ equals resistance × capacitance and is expressed in seconds when SI units are used.
- After one τ, the capacitor charges to ~63.2% of its final voltage; after 5τ it is above 99%.
- Designers often choose τ to set cutoff frequencies in RC filters, using f_c = 1/(2πRC).