The Iowa State College subcritical assembly is a natural uranium-graphite pile constructed as a teaching tool to illustrate the principles of nuclear physics and engineering and as a facility for graduate thesis research in nuclear engineering. The determination of the basic operating characteristics of this assembly is described and discussed. The material buckling as determined from flux measurements was the parameter used in comparing the results. Tests were conducted for the 6 in., in., and 12 in. lattice arrangements and for all uranium removed. Tests were made with air and water in the coolant annuli surrounding the uranium slugs. Bucklings were calculated using the elementary theory of Murray (in which all extraneous materials are treated as poisons) and the method of Volkoff and Rumsey (in which the moderating effect of the water and the shielding effects of the various materials are considered) for the three lattice arrangements, and they are compared with the experimental results. The position of the neutron sources in the source compartment and the presence of water around the sources were found to affect the measured value of material buckling.