We analyze the statistical characteristics of quasinonequilibrium two-dimensional electron-hole plasmas in graphene layers (GLs) and graphene bilayers (GBLs) and evaluate their heat capacity. The GL heat capacity of the weakly pumped intrinsic or weakly doped GLs normalized by the Boltzmann constant is equal to cGL≃6.58. With varying carrier temperature the intrinsic GBL carrier heat capacity cGBL changes from cGBL≃2.37 at T 300 K to cGBL≃6.58 at elevated temperatures. These values are markedly different from the heat capacity of classical two-dimensional carriers with c=1. The obtained results can be useful for the optimization of different GL- and GBL-based high-speed devices.