Capacitor Energy And Time Constant Calculator - Calculate the energy (E) and time constant (RC) in a capacitor for a given voltage across it using an online capacitor energy (E) and RC time constant calculator. The capacitor energy and time constant calculator can be used to calculate two different values: the time constant (T) can be calculated using the values of capacitance (C) and load resistance (R), and the energy stored in a capacitor (E) can be calculated using all three inputs: voltage (V), capacitance, and load resistance.