A method for use by a placement and routing tool automatically selects positions for all n I/O buffers of an IC from among a set of m available legal positions for such buffers within an IC layout so as to best meet a set of criteria affected by I/O buffer placement. The method initially establishes a weighted cost function c_i,j quantifying a cost, relative to that set of criteria, of assigning the i^th I/O buffer to the j^th legal position. The weighted cost function is then evaluated with respect to each possible combination of i and j to produce an mn cost data matrix indicating all costs associated with all of the mn possible I/O buffer placements. The cost data matrix is then analyzed to produce a placement plan assigning each I/O buffer to a separate legal position in a way that minimizes a total cost of the buffer placement with respect to the set of criteria. The method may also be used to assign I/O pads among a set of legal pad positions.