Editing Growth–share matrix (section)

===Relative market share===
This indicates likely cash generation, because the higher the share the more cash will be generated. As a result of 'economies of scale' (a basic assumption of the BCG Matrix), it is assumed that these earnings will grow faster the higher the share. The exact measure is the brand's share relative to its largest competitor. Thus, if the brand had a share of 20 percent, and the largest competitor had the same, the ratio would be 1:1. If the largest competitor had a share of 60 percent, however, the ratio would be 1:3, implying that the organization's brand was in a relatively weak position. If the largest competitor only had a share of 5 percent, the ratio would be 4:1, implying that the brand owned was in a relatively strong position, which might be reflected in profits and cash flows. If this technique is used in practice, this scale is logarithmic, not linear.

On the other hand, exactly what is a high relative share is a matter of some debate. The best evidence is that the most stable position (at least in [[fast-moving consumer goods]] markets) is for the brand leader to have a share double that of the second brand, and triple that of the third. Brand leaders in this position tend to be very stable—and profitable; the Rule of 123.

The selection of the relative market share metric was based upon its relationship to the experience curve. The market leader would have greater experience curve benefits, which delivers a cost leadership advantage.

Another reason for choosing relative market share, rather than just profits, is that it carries more information than just cash flow. It shows where the brand is positioned against its main competitors, and indicates where it might be likely to go in the future. It can also show what type of marketing activities might be expected to be effective. {{Citation needed|date=February 2009}}