RC Time Constant Calculator
Choose a mode and units. Enter signed initial and final voltages for a step response.
A QUICK WALKTHROUGH
How to use this tool
- Select time constants, target voltage, response fraction, or elapsed time.
- Enter resistance, capacitance, units and the required voltage or time inputs.
- Read τ, 5τ and the five-row voltage and fraction table; save the complete report.
Scope
The ideal first-order response is V(t)=Vi+(Vs−Vi)(1−exp(−t/τ)), Q=CV. The completed fraction measures progress from Vi to Vs, including discharge; it is not absolute capacitor charge. Equal endpoints give a static voltage and no unique target time. Final voltage is asymptotic. Excludes tolerances, loading, leakage and other dynamics; 5τ is not guaranteed settling.
GOOD TO KNOW
Common questions
Are these equipment specifications?
No. These results describe the stated mathematical model and user inputs.