A simple reliable method to measure Residual Adsorption Capacity (RAC) of charcoal adsorbers on which a gas is physisorbed has been developed. The method consists of passing a pulse of weakly adsorbed gas(es) through the adsorption filter(s) and measuring the retention time. This retention time is then correlated to the residual adsorption capacity. In order to predict the retention time‐RAC relationship for filters with various configurations and bulk densities, this pulse test was mathematically modeled. The numerical solution of the model involved estimating the transport rate parameters, using existing correlations and the moment technique. A perturbation analysis indicated that the accuracy of the model is closely associated with the estimates of adsorption equilibrium constant and the intraparticle diffusion coefficient of the test gas. The model is shown to be accurate in predicting the RAC of an adsorber under dry and humid conditions from a limited data set.