This paper presents a comparative analysis of measuring firm size and its implications for their political activity. It decomposes the measurement for large firms and analyses systematically different ranking methods and their application across countries. We hypothesize that criteria for measuring size impact on the ranking results and we propose a new index for firm size. Moreover we analyse how different composite indexes of measuring firm size introduce a rank bias by sector and how different size measures impact on the level of political activity. The paper uses a new original data set on large firms from Germany, USA and United Kingdom and the analysis presented brings a contribution to the literature on firms’ size and their political activity in the form of lobbying or social corporate responsibility.
