A 100-V ac energy meter based on the system-on-a-film (SoF) concept, in which various devices are integrated on a flexible film, is presented. The system consists of 20-V organic CMOS digital and analog circuits with a floating gate (FG) for process variation compensation, 100-V organic pMOS rectifiers for generating a 50-Hz clock and 20-V dc power, and an organic LED (OLED) bar indicator. The energy meter based on the SoF is flexible and therefore can be installed to monitor each ac outlet simultaneously. The organic devices are printable, and it is expected that they can be formed using a low-cost printing process in the future. The energy meter can measure the accumulated energy of a 100-Vrms ac lineup to a full-scale value of 360 Wh when a 500-W target load is monitored. The flexible film is foldable and its total area excluding the ac connector is 200 × 200 mm2 in the unfolded form or 70 × 70 mm2 when folded.