A method is described for adapting the size of data for a future Transmission Time Interval (TTI) by a User Equipment (UE), wherein all the Media Access Control (MAC)-d flows are grouped and stored in different lists based on a type of grants associated with the MAC-d flows, ability of a MAC-d flow to be multiplexed with another MAC-d flow from a list, and data availability in a logical channel mapped onto a MAC-d flow in the current TTI. The E-TFC is then selected by the UE for the future TTI using the MAC-d flow having the highest power offset in a consolidated list including the grouped MAC-d flows. The size of the data is thereby adapted using the selected E-TFC. Further disclosed is a method for generating RLC PDUs by the UE for the future TTI using the variation in the scheduled grant for the UE and the size of the data adapted for the future TTI.