Amount is used of things involving a unified mass— bulk, weight, or sums. In accounting, it has the same meaning as total; generally, it is safe to use amount to refer to anything which can be measured. Number is correctly used to refer to items which can be counted in individual units."What is the amount of the bill?" "He has left only a small amount of food." "Joe has a number of old suits for sale."
Dictionary of problem words and expressions. Harry Shaw. 1975.