This paper describes and compares methods for measuring the time of emergence and the pattern of emergence of Pipistrellus pipistrellus from its summer nursery roost. The time of first emergence was a poor statistic with which to describe the emergence time of the whole roost compared with either the median or mean emergence times. ‘Outburst activity’, whereby bats cluster in their emergence, can be recorded by counting the emergence rate per second. Using the log survivor function, clustering during emergence can be quantified. The degree of clustering appeared to be positively related to the total number of bats emerging from the roost.