Quantity demanded is an economic measurement of demand for goods or services over a period of time. The price of a product and demand for that product have an inverse relationship, according to the law of demand. As the price of a product decreases, its demand will increase and vice versa. There isn’t a 1:1 relationship between the increase/decrease in the price of a product and the increase/decrease in demand for that product. The change in price that affects demand is called elasticity of demand.