The value of a stamp is determined by several factors. First of all, it is rareness. According to the law of demand and supply, if there is a lot of people want a stamp, the value of it goes up a great deal. And the harder a stamp is found on the market, the more valuable it is.  In addition, the value is also determined by condition and grade.  Grade is about how well the stamp’s design is centered between the perforations, both horizontally and vertically. Condition is about the physical characteristics of the stamp’s paper, including ink, color, and gum in the case of mint stamps.