Abstract: National policy ambition plays a central role in climate change governance under the Paris Agreement and is now a focus of rapidly emerging literature. In this contribution, we argue that policy ambition can be captured by the level of national policy activity, which in accordance with the existing literature should be referred to as “policy density.” In this study, we measure climate policy density by drawing on three publicly available databases. All three measurements show an upward trend in the adoption of climate policy. However, our empirical comparison also reveals differences between the measurements with regard to the degree of policy expansion and sectoral coverage, which are due to differences in the type of policies in the databases. For the first time, we compare the patterns of policy density within each database (2000–2019) and reveal that while they are different, they are nonetheless potentially complementary. Since the choice of the database and the resulting measurement of policy density ultimately depend on the questions posed by researchers, we conclude by discussing whether some questions are better answered by some measurements than others.