Justice as proportion: The distribution of g between individuals a and b is just when:

S(g,a)		S(g,b)	g may be: pay, health care military duty, pie, education, basketball tickets, food, etc.
——	=	——
F(g,a)		F(g,b)

where S(g,x) is the share (i.e. how much) of the good (benefit) or burden (call it "g") x gets.

Examples of possible functions F:

F(g,x) = constant (same for all x)
F(g,x) = how much x needs g.
F(g,x) = how much g x has a right to
F(g,x) = how much effort x put out
F(g,x) = x's contribution to society
F(g,x) = x's ability to provide g
F(g,x) = how much x pays for g

So justice (on this Aristotelian view) is a kind of equality, an equality of proportion.

The distribution of g is just when S(g,x)/F(g,x) is constant (equal) over x.

Marx: From each according to his ability; to each according to his need.