Elo ratings are FiveThirtyEight’s favorite method for comparing teams across different eras — we’ve previously used them to explore the history of the NBA and NFL. The ratings are an intentionally simple measure of team strength based on the final score, location and date of a team’s games. Now we’ve calculated them for 89 franchises across 146 years of baseball history — more than 400,000 ratings in total.
Elo is calibrated so that an average MLB team has a rating of around 1500, although the actual league average depends on how recently expansion teams (which start with a 1450 rating) were added.