Cube dimensions and strength
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 equivalent.
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 The Dutch standard NEN 5950 (now superceded by EN 206) had standard cube test specimen of 150mm but allowed the use other cube sizes with a correction factor applied of 0.91 for 100mm cubes, 1.05 for 200mm cubes.
A correction factor is not used in the European standard. 100, 150 or 200mm cubes can be used without correction to the compressive strength obtained from the test when checking for strength class conformity.