The present disclosure relates to selecting a Transport Block Size (TBS) in a communication system. An aspect is directed to an apparatus for selecting a Transport Block Size (TBS) for a transmitter of a communication system. The communication system supports variable Transmission Time Interval (TTI) lengths with respect to the number of symbols to be transmitted in one TTI. The apparatus is configured to receive first information indicating a TTI length, receive second information indicating a number of reference symbols included in the TTI, decode the TTI length from the first information, and decode the number of reference symbols included in the TTI from the second information. The apparatus is further configured to calculate a number of data symbols included in the TTI based on the TTI length and based on the number of reference symbols included in the TTI, calculate a number of data Resource Elements (REs) in the TTI based on the allocated bandwidth and based on the number of data symbols included in the TTI, and select a TBS from the data structure based on the calculated number of data REs. Further aspects of the present disclosure relate to a base station, a UE, a method, a computer program, a computer-readable recording medium, and a system.