Pi theorem

(Or Buckingham Pi theory.) The basis for dimensional analysis.

The theorem states that an equation for a physical system that can be written f(Q₁, Q₂, . . . , Q_m) = 0 can also be written as g(π₁, π₂, . . . , π_{m - n}) = 0 where Q_i are m dimensional parameters, numbers, and variables; π_i are m - n nondimensional quantities; and n is the number of fundamental dimensional units.