The concrete structural code Eurocode 2 (BS EN 1992) is based on cylinder compressive strength. A relationship between the strength of 150mm diameter cylinders of 300mm length and 150mm cubes is given and is adopted by EN 206. In the UK, BS 8500 states that the compressive strength of 150mm cubes and 100mm cubes are considered equivelant.
This has been assumed for some time although there are references that would beg to differ. Neville, Properties of concrete 4th edition, reports that a 150mm cube is 96% the strength of a 100mm cube. The Dutch standard NEN 5950 (now superceded by EN 206) has standard cube test specimen of 150mm but allows the use other cube sizes where a correction factor is applied of 0.91 for 100mm cubes, 1.05 for 200mm cubes.
A correction factor is not used in the European standard and 100, 150 or 200mm cubes can be used without correction to the compressive strength obtained from the test when checking for strength class conformity.