Experiments involving RC circuits are an integral part of introductory physics courses. Previous articles using RC circuits describe determining the charge on a Van de Graaff generator, measuring currents and voltages in a charging RC circuit using a multimeter or an Arduino, measuring the decay constants of complex RC circuits, and using the Pasco ScienceWorkshop 750 Interface to examine various physical properties of capacitors. In this paper, I will show how to determine the capacitance of a capacitor charged with a battery of known voltage using an RC circuit and numerical integration performed on a spreadsheet.