Experiments are reported in which subjects were asked to indicate when they felt 15 minutes had passed while observing each of two model environments of similar design but differing spatial scale. Three types of model environment were used: scale model railways, sitting room models, and abstract, non-representional environments. Subject's judgments of duration were significantly shorter in the smaller of the two model environments in every case except where comparisons were made with the smallest scale models of room interiors. It is suggested that the effect of spatial scale on duration judgments is related to differences in the density of the information to be processed in environments of different scale. It is further suggested that there may be an optimum value for information density related both to the scale and to the type of environment being modelled.