Determining the optimal amount of public goods requires the determination of their demand. Their demand gets depicted by the price/quantity concepts that indicate the price individuals are ready to pay for an additional commodity unit of each quantity. On the other hand, the demand curve for private goods gets horizontally summarized, unlike the public goods' demand curves that are vertically summarized. Due to this, the public good's demand curve shows what price the society is willing to part with for a particular commodity.

The demand curves for public goods get derived differently from those of private goods as their demands are also derived differently. Because of the non-competitive nature of public goods, any individual in the market can consume every unit. These goods possess a fixed quantity in the market, where every individual in the market agrees to consume the same quantity of the good. The issue is, however, the willingness of these individuals to pay for these goods are different.