What is my mmr? Top 3 places to check mmr
League of Legends uses a number called MMR, or MatchMaking Rating, to indicate a player's skill level. For each game style, a different opponent is chosen based on your MMR. Different websites monitor just non-premade solo games played in ranked, regular, and ARAM queues. Visit Riot's website to learn more about MMR. Here’s a brief description of what MMR is.
Source: india.com