Study Aim: This paper tries to grapple with some of the questions about counting numbers in the sex industry as an adjunct to a much larger sociological study of the ways in which digital technology has changed the commercial sex industry. The project sets out to reflect on the ethics of counting online and what this means to the sex work community. Method: The data is provided by the largest online adult services advertising platform in the UK which is compared to our own counts of sex worker profiles on that same platform to illustrate some of the challenges related to counting the sex industry. Result: The data comparisons show that using front facing public profiles of adult sex workers is not an accurate measure of the size of the sex industry, and whilst the information can be used for some purposes it must be used with caution. The findings point to the need for researchers and others involved in mapping sex worker populations to reflect carefully on ethical issues and the impact of mapping on sex workers. Conclusion: It is suggested that the usefulness of counting profiles on adult websites should be approached with caution both as a researcher analyst and also as someone who uses or requests this form of quantification. With over 40% differences between outward facing and active profiles the margins for error are high.