Research into risk communication has commonly highlighted the disparity between the meaning intended by the communicator and what is understood by the recipient. Such miscommunications will have implications for perceived trust and expertise of the communicator, but it is not known whether this differs according to the communication format. We examined the effect of using verbal, numerical and mixed formats on perceptions of credibility and correctness, as well as whether they influenced a decision to evacuate, both before and after an ‘erroneous’ prediction (i.e. an ‘unlikely’ event occurs, or a ‘likely’ event does not occur). We observed no effect of communication format on any of the measures pre-outcome, but found the numerical format was perceived as less incorrect, as well as more credible than the other formats after an ‘erroneous’ prediction, but only when low probability expressions were used. Our findings suggest numbers should be used in consequential risk communications.