The cube test is the test most commonly used for determining concrete strength in the UK. A 150mm (6 in.) cube of concrete is cast, is cured for the appropriate time (see Concrete Age at Testing), and is then compressed between two parallel faces. The stress at failure is taken to be the compressive strength of the concrete.
Generally the cube test gives higher compressive strengths than the alternative cylinder test. See Conversion between Cube and Cylinder Strengths.
The exact procedures for the cube test are laid down in Parts 107, 108 and 116 of BS1882 (see References 12, 13 and 14).