Time Constant (𝜏)
the time it takes for the initial membrane voltage (Vm)
to decline by \(1 - \left(\frac{1}{e}\right)\) or around 63%
Calculate Time Constant from Resistance and Capacitance
$$\tau = Resistance_{membrane} * Capacitance_{membrane}$$
Calculate Time Constant from Capacitance and Diameter
$$\tau = \frac{Capacitance\ of\ Membrane\ (C_m)(Farads)}{\pi * diameter}$$