Waste coffee grounds were activated by KOH at various pyrolysis temperatures, changing the ratio of the area of the mesoporous structure to that of the microporous structure, the surface area, the amount of oxygen and nitrogen functional groups in the grounds, and their chemical structure. At a pyrolysis temperature of 700 °C, the KOH-activated waste coffee grounds had a specific capacitance of 175 F g−1 at 1 A g−1 and 475 F g−1 at 0.1 A g−1 from the discharge profiles. Assembling the KOH-activated waste coffee grounds in a coin cell yielded an energy density and power density of 11 W h kg−1 and 7500 W kg−1, respectively, with an operating potential of 1.5 V, making waste coffee grounds a viable feedstock for manufacturing energy materials. Copyright 2016 The Society of Powder Technology Japan