Various aspects of the present disclosure generally relate to wireless communication. In some aspects, a user equipment (UE) may obtain a nominal resource block value associated with one or more allocated subchannels for a sidelink communication. The UE may identify a number of physical sidelink shared channel (PSSCH) resource elements to be used for a transport block size calculation based at least in part on the nominal resource block value. The UE may transmit the sidelink communication, and reserve one or more resources for one or more respective retransmissions of the sidelink communication, based at least in part on the number of PSSCH resource elements. Numerous other aspects are described.