Organisms acquire and use information from their environment to guide their behaviour. However, it is unclear whether this information quantitatively limits their performance at behavioural tasks. Here we relate information to the ability of Escherichia coli to navigate up chemical gradients, the behaviour known as chemotaxis. First, we derive a theoretical limit on the speed with which cells climb gradients, given the rate at which they acquire information. Next, we measure cells’ gradient-climbing speeds and the rate of information acquisition by their chemotaxis signalling pathway. We find that E. coli cells make behavioural decisions with much less than the one bit required to determine whether they are swimming up the gradient. Some of this information is irrelevant to gradient climbing, and some is lost in communication to behaviour. Despite these limitations, E. coli cells climb gradients at speeds within a factor of two of the theoretical bound. Thus, information can limit the performance of an organism, and sensory–motor pathways may have evolved to efficiently use information acquired from the environment.