Gerrymandering is the drawing of political districts to gain advantage beyond what would accrue by natural patterns of population. Gerrymandering can benefit an individual legislator or a whole political party. This site is principally concerned with partisan gerrymandering, the establishment of an overall advantage across an entire state.
Partisan gerrymandering is considered justiciable by the United States Supreme Court, but a nationwide standard has not been established. Below are online calculators for simple statistical tests described in "Three Tests for Practical Evaluation of Partisan Gerrymandering," by Samuel S.-H. Wang, 68 Stanford Law Review 1263 (2016). This approach was awarded a prize in Common Cause's 2016 First Amendment Gerrymander Standard Writing Competition.