Abstract A classic result of psychophysics is that human perceptual estimates are more variable for larger magnitudes. This “Weber behavior,” however, has typically not been the focus of the prominent Bayesian paradigm. Here, we examine the variability of a Bayesian observer in comparison with human subjects. In two preregistered experiments, we manipulate the prior distribution and the reward function in a numerosity-estimation task. When large numerosities are more frequent or more rewarding, the Bayesian observ…