Fibre reinforced polymer (FRP) composites are more and more used in the building trade for the set up of reinforcing and repair devices. As known, FRP composites offer higher strength and Young modulus than traditional steel devices, but the FRP reinforcement is a passive one, that is it begins working as the stress state of the member grows. Moreover, when confining compressed pillars with FRP composites, the effective contribution of the composite cannot be accurately evaluated. In the present paper, some theoretical relationships available in literature and in CNR-DT200 2004 are analyzed, regarding the evaluation of confinement effect on wrapped concrete and masonry columns. The reliability of these formulations is investigated, comparing the theoretical values with experimental test results on wrapped or unwrapped brickwork and concrete samples. Interesting observations can be made about the material behaviour, the specimens failure modes and the effective confinement action produced.