In this study we aimed to resolve the now decades-long debate on how the structure of nanoporous carbons electrodes impacts their capacitive energy storage. Electrochemistry measurements on a large series of commercial activated carbons showed no clear correlation between capacitance and pore size, nor between capacitance and specific surface area. In contrast, NMR spectroscopy 240 experiments and modelling revealed a strong correlation between capacitance and electrode structural disorder for both the commercial porous carbons as well as their thermally annealed counterparts. Carbons with smaller ordered domains have higher capacitances, which we attribute to their more efficient storage of ions in the carbon nanopores. Overall, this work reveals a previously overlooked structural factor that determines the capacitance of nanoporous carbons. Our 245 findings will guide the design and synthesis of improved electrode materials for EDLCs and will motivate fundamental research on how disorder impacts charge storage. Free-standing carbon films were made by mixing carbon powder (95 wt %) and polytetrafluoroethylene binder (5 wt %) in ethanol. The films were manually rolled into a similar thickness (approximately 0.25 mm). The films were dried in a vacuum oven at 100 ℃ for at least 24 h before use to fully remove the residual ethanol and water.