Methods, systems, and devices for wireless communications are described. In some systems, two devices may communicate over a sidelink and support a mutually understood transport block (TB) size (TBS) determination procedure associated with a data channel including a control message. A first device may encode and transmit information on the data channel, including the control message and a data message. A second device may receive and decode the information on the data channel. The first device and the second device may determine a TBS for encoding and decoding the data channel, respectively, based on determining an estimated resource element (RE) overhead for the control message and determining an approximate TBS based on the estimated RE overhead.