Board Thread:Questions and Answers/@comment-107.202.42.60-20160325234539/@comment-24407809-20160326065740

I assume your question refers to the "Titan kills" section of Eren and Levi's character boxes. Those numbers are taken from kills either seen on-panel, or from kills that are mentioned during the story (like the kills for Oluo, Petra, Eld, and Gunther). Currently, Eren has killed more Titans than Levi (or, indeed, anyone) on-panel, though this is counting his kills in Titan form.