size package:fgl

size :: Graph gr => gr a b -> Int
fgl Data.Graph.Inductive.Graph
The number of edges in the graph. Note that this counts every edge found, so if you are representing an unordered graph by having each edge mirrored this will be incorrect. If you created an unordered graph by either mirroring every edge (including loops!) or using the undir function in Data.Graph.Inductive.Basic then you can safely halve the value returned by this.
defaultGraphSize :: Int
fgl Data.Graph.Inductive.Monad.IOArray Data.Graph.Inductive.Monad.STArray
indepSize :: DynGraph gr => gr a b -> ([Node], Int)
fgl Data.Graph.Inductive.Query.Indep
The maximum independent node set along with its size.