How it works
Time constant τ=RC. Charging reaches 63.2% after τ; 95% after −ln(0.05)τ and 99% after −ln(0.01)τ.
Input definitions
- Resistance (kΩ)
- Enter the value in the labeled unit.
- Capacitance (µF)
- Enter the value in the labeled unit.
A worked example
- Resistance (kΩ)
- 10
- Capacitance (µF)
- 100
Assumptions & limits
Ideal step input, initially uncharged capacitor, fixed R and C. No leakage, source impedance or component tolerance.
Sources & review
Maintained by AnsRio. Methods and examples use automated checks; this does not imply independent professional certification.
Method updated 2026-10-17. Content checked against the stated method and examples. Our verification approach.
Common questions
Is a capacitor fully charged after five time constants?
An ideal RC charge reaches 1−e⁻⁵, about 99.33%, after five time constants. It approaches the final voltage asymptotically rather than reaching it exactly.
Does this replace a circuit or electrical safety assessment?
No. The result uses the idealized model shown. Component tolerance, temperature, fault conditions and installation requirements need separate evaluation.
How does the RC time constant and settling time tool work?
Time constant τ=RC. Charging reaches 63.2% after τ; 95% after −ln(0.05)τ and 99% after −ln(0.01)τ.
What are the assumptions and limits of RC time constant and settling time?
Ideal step input, initially uncharged capacitor, fixed R and C. No leakage, source impedance or component tolerance.