This review considers the various components which determine the total energy requirement of a product. A method which may be used by a designer to calculate the total energy requirement of a product, in a more appropriate manner than methods previously published, is described. With the proposed method the advantage of recycling materials from discarded products results in a lower energy requirement. Two examples are given to illustrate the calculation method. The first is a comparison of the energy used, in manufacturing hexagon head bolts by extrusion and cutting whilst the second concerns the energy commitments involved in substituting aluminium alloys for steel and cast iron parts in automobiles.