The diameter of core specimens for the determination of concrete compressive strength should preferably be at least three times the nominal maximum size of the coarse aggregate used in the concrete, and must be at least twice the maximum size of the coarse aggregate in the core sample. The length of the specimen, when capped, should be nearly as practicable twice its diameter. A core having a maximum height of less than 95% of its diameter before capping or a height less than its diameter after capping must be rejected. It is preferable to test the cores in moist condition.