# Time constant τ calculation

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

On this page you can calculate the time constant, resistance or capacitor of a resistor and a capacitor circuit.

Time constant calculator

 What should be calculated? Time constant Capacitor Resistor Input Capacitor F mF µF nF pF Resistor mΩ Ω kΩ MΩ Time constant pSec nSec µSec mSec Sec Result Capacitor Resistor Time constant Decimal places 0 1 2 3 4 6 8 10

#### 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%.

$$\displaystyle Τ=R ·C$$         $$\displaystyle R=\frac{Τ}{C}$$         $$\displaystyle C=\frac{Τ}{R}$$

#### Legend

 $$\displaystyle R$$ Resistor $$\displaystyle C$$ Capacitor Τ Time constants