The newtonPolytope of f is the convex hull of its exponent vectors in n-space, where n is the number of variables in the ring.
Consider the Vandermond determinant in 3 variables:
i1 : R = QQ[a,b,c]
o1 = R
o1 : PolynomialRing
i2 : f = (a-b)*(a-c)*(b-c)
2 2 2 2 2 2
o2 = a b - a*b - a c + b c + a*c - b*c
o2 : R
If we compute the Newton polytope we get a hexagon in QQ^3.