Micron‐sized particles (0.3 to 15 &mgr; in radius) of metals such as aluminum, carbonyl nickel, molybdenum; semiconductors such as magnetite and zirconium hydride; and insulators such as aluminum oxide, silicon oxide, and eccospheres are charged by contact electrification in electric fields up to 8000 V in a 0.3‐cm gap. The charges are measured with a drift‐tube detector and a quadrupole mass spectrometer and compared with a theoretical value which includes the contact potential and the electric field. Experimentally, the contact charge is quite important for particles less than one micron in radius, but relatively unimportant for larger particles. The experimental values are in good agreement with the calculated values for the range of materials and particle sizes studied.