Your files stay on your device

# RC time constant calculator

Computes the RC time constant, charge and discharge times to a target percentage, and the cutoff, gain, and phase of an RC filter.

Enter a resistor and a capacitor to time them.

tau = R times C is the time a capacitor takes to reach 63.2 percent of the supply, and it is a proportionality: two tau is 86.5 percent, three is 95 percent, five is 99.3. The same tau sets the filter cutoff at 1/(2 pi RC), where gain is 3 dB down and phase is 45 degrees. This is the ideal first-order model. It stops being true once electrolytic ESR, dielectric absorption, or DC-bias derating enter the picture, and real capacitors lose a lot of their marked value near their voltage limit.
Options

## More unit & math tools

- [555 timer calculator](/converters/555-timer-calculator)
- [4-20 mA scaling](/converters/4-20ma-scaling-calculator)
- [Unit converter](/converters/units)
[All unit & math tools](/converters)

Was this tool useful?
YesNo

---

Canonical HTML: https://nutter.tools/converters/rc-time-constant-calculator
Markdown version: https://nutter.tools/converters/rc-time-constant-calculator.md
Plain-text version: https://nutter.tools/converters/rc-time-constant-calculator.txt
Agent index: https://nutter.tools/llms.txt