Depending on practical considerations and standards, different types of test specimens are used for the determination of the uniaxial compressive strength of concrete. Appropriate conversion factors, also referred to as shape factors, are needed to convert the compressive strength as determined on one type of specimen to the equivalent compressive strength of another type of specimen. As such shape factors for vibrated concrete are influenced by the composition of the concrete, questions arise concerning the factors that affect the shape factors for powder-type self-compacting concrete (SCC). This paper describes the findings of an extensive research programme performed by three laboratories on the influencing parameters of the shape factors for SCC. Concrete composition parameters such as powder content, cement/powder ratio, water/cement ratio and the type of coarse aggregates, cement, filler and plasticiser appear to have little effect on the experimentally obtained shape factors. Any possible influence on compressive strength was overshadowed by experimental scatter