Disclosed is a method performed by a user equipment (UE) in a communication system, including receiving, from a base station, downlink control information (DCI) including resource assignment information for a physical downlink shared channel (PDSCH); identifying a number of resource elements (REs) allocated for the PDSCH based on a number symbols for the PDSCH and a number of allocated physical resource blocks (PRBs), wherein a number of REs for a demodulation reference signal (DMRS) is excluded from the number of REs allocated for the PDSCH; identifying intermediate information based on the number of REs allocated for the PDSCH; identifying a transport block size (TBS) based on quantized intermediate information; and receiving, from the base station, the PDSCH based on the TBS.