The skewness of a graph 
is the minimum number of edges whose removal results in a
planar graph (Harary 1994, p. 124). The skewness
is sometimes denoted 
(Cimikowski 1992).
A graph 
with 
has toroidal crossing number 
. (However, there exist graphs with 
that still have 
.)
satisfies
 |
(1)
|
where 
is the vertex count of 
and 
its edge count (Cimikowski 1992).
The skewness of a disconnected graph is equal to the sum of skewnesses of its connected components.
The skewness of a complete graph 
is given by
 |
(2)
|
of the complete bipartite graph 
by
 |
(3)
|
and of the hypercube graph 
by
 |
(4)
|
(Cimikowski 1992).
