How do you calculate excess capacity in monopolistic competition?

Excess capacity in monopolistic competition is calculated by comparing the output level at which firms operate to the output level that would minimize average total costs (the efficient scale). In a monopolistically competitive market, firms typically produce less than this efficient scale, leading to excess capacity. This can be quantitatively assessed by determining the difference between the quantity produced at the profit-maximizing level (where marginal cost equals marginal revenue) and the quantity that would minimize average costs. The resulting difference indicates the excess capacity present in the market.