RL Time Constant Calculator
Work out an RL circuit time constant from inductance and resistance.
Runs in your browser. Nothing is uploaded — your input is processed on this device and discarded when you close the tab.
RL Time Constant Calculator
How to use this tool
- Enter the inductance in henrys.
- Enter the resistance in ohms.
- Press Generate to see the time constant in seconds and milliseconds.
Worked example
With inductance 0.5 henrys and resistance 100 ohms, the time constant is 0.5 / 100 = 0.005 seconds, which is 5 milliseconds.
What this tool does not do / Limits
This is the ideal series RL formula only. It ignores resistance in the inductor itself, core saturation, parasitic capacitance and component tolerances, so treat the result as an estimate and check the datasheet for real parts.
Frequently asked questions
What happens after one time constant?
In a charging RL circuit the current reaches about 63.2% of its final value after one time constant.
What about five time constants?
After about five time constants the current is over 99% of its final value, which is often treated as settled.
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