In queueing theory, a discipline within the mathematical theory of probability, Kingman's formula is an approximation for the mean waiting time in a G/G/1 queue. The formula is the product of three terms which depend on utilization, variability and service time. It was first published by John Kingman in his 1961 paper The single server queue in heavy traffic. It is known to be generally very accurate, especially for a system operating close to saturation.