Since the 1970s, catalogs of protest events have been at the heart of research on social movements. To measure how protest changes over time or varies across space, sociologists usually count the frequency of events, as either the dependent variable or a key independent variable. An alternative is to count the number of participants in protest. This article investigates demonstrations, strikes, and riots. Their size distributions manifest enormous variation. Most events are small, but a few large events contribute the majority of protesters. When events are aggregated by year or by city, the correlation between total participation and event frequency is low or modest. The choice of how to quantify protest is therefore vital; findings from one measure are unlikely to apply to another. The fact that the bulk of participation comes from large events has positive implications for the compilation of event catalogs. Rather than worrying about the underreporting of small events, concentrate on recording large ones accurately.