Mean Reciprocal Rank is a measure to evaluate systems that return a ranked list of answers to queries.

For a single query, the reciprocal rank is $\frac{1}{rank}$ where $rank$ is the position of the highest-ranked answer ($1,2,3,\dots ,N$ for $N$ answers returned in a query). If no correct answer was returned in the query, then the reciprocal rank is 0.

For multiple queries $Q$, the Mean Reciprocal Rank is the mean of the $Q$ reciprocal ranks.

$$MRR=\frac{1}{Q}\sum _{i=1}^Q\frac{1}{{rank}_i}$$