Scaling relations are developed to allow estimation of the atomic hydrogen concentration at the substrate during diamond chemical‐vapor deposition for both diffusion‐dominated and convection‐dominated reactors. In the convection‐dominated case, it is shown that there exists an optimal Mach number which maximizes the H concentration delivered to the substrate. In addition, when homogeneous recombination is taken into account, there exists an optimal operating pressure. This analysis shows that a sonic flow of highly dissociated hydrogen at a pressure near atmospheric is optimal for rapid growth of high‐quality diamond.