Comparative testing reveals that high strength concrete (HSC) compressive strength values are greater by 5% when measured on 100 x 200 mm specimens. Moreover, the coefficient of variation on one set of three 100 x 200 mm specimens is as small as, or smaller than that for 150 x 300 mm specimens. Furthermore, a high performance capping compound testing 60 to 70 MPa using 50-mm cubes has proved to be effective when used for testing HSC up to 120 MPa due to the confinement of the capping compound between the platen and the specimen, but the capping layer has to be less than 3 mm thick. Under these conditions, the results are similar to those obtained when the ends are faced by grinding. Nevertheless, it is safer to grind the specimen ends when the strength of the concrete exceeds 100 MPa. It is shown that eccentricity of less then 4 mm between the testing machine and specimen axis does not affect the compressive strength values.