A high-school third-year or undergraduate first-semester general chemistry laboratory experiment introducing simple-cubic, face-centered cubic, body-centered cubic, and hexagonal closest packing unit cells is presented. Latex balls and acrylic resin plates are employed to make each atomic arrangement. The volume of the vacant space in each cell is measured by weighing water poured into the unit cell model, and the packing efficiency of each unit is obtained from the volume of vacant space. The observed values are compared with the theoretical calculations. Students can easily understand experimentally and theoretically that the packing efficiency of the face-centered cubic is the same as that of the hexagonal closest packing and significantly greater than that of the body-centered cubic. Moreover, they can understand the number of the neighboring atoms for any atom (coordination number) in each cell.