Time constant τ calculation

Online calculator and formulas for calculating the time constant τ (tau) of resistor and capacitor

Calculation of the time constant

This function calculates the time constant Τ of an RC circuit, or its capacitor, or its resistance. Two of the values must be known in order to calculate the third one. Use the radio button to select which value should be calculated and enter the known values. Then click on the 'Calculate' button.

Time constant calculator

  What should be calculated?
Time constant
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Time constant

Formula for calculating the time constant

The time constant of an RC element (low pass) is the product of R * C. Its unit of measurement is seconds. The symbol is the Greek letter Τ (tau)

The time constant is required to calculate the state of charge at a specific point in time when charging or discharging the capacitor.

After a period of 3 time constants, the output signal has approx. 95% of the size of the input signal. After 5 Τ the charge is approx. 99.3%.

\(\displaystyle Τ=R ·C\)         \(\displaystyle R=\frac{Τ}{C}\)         \(\displaystyle C=\frac{Τ}{R}\)


\(\displaystyle R\)


\(\displaystyle C\)



Time constants

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