The beam-to-column joints are often described as pinned or rigid. Due to the effect of the joint details, the joint may be defined as semi-rigid one. In Eurocode3, Annex J, the value of the initial rotational stiffness of the joint can be estimated. In this paper, variety of steel and composite joint details are classified and demonstrated. Depending on Eurocode3 and some realistic assumptions for these details, formulae to calculate the initial rotational stiffness are predicted and tabulated. Comparisons between the results of the present predicted formulae and those obtained from the Module Bank System, for semi-rigid joints, show the accuracy yet simplicity of the present work. It is also recommended to implement these formulae by the Egyptian code committee in order to be used for pre-design purposes.