The cluster spans approximately how many light-years across, dwarfing the Milky Way's width?

Answer

20 million light-years

The Coma Cluster spans a massive physical diameter estimated to be roughly 20 million light-years across.

The cluster spans approximately how many light-years across, dwarfing the Milky Way's width?
Spaceastronomygalaxy clusterComa ClusterCoordinatesGalactic Coordinates