Determining the result using a direct quantity measurement is fundamental for the most varied purposes in the scientific and technological fields. However, it is expected to establish the value of a quantity indirectly, that is, from the mathematical operations that combine previously defined results of two or more quantities. For example, we cite the volume of a parallelepiped calculated from the product on its sides, the projectile’s speed determined by the ratio between the distance traveled and the flight time, or the electrical power (voltage and current product) dissipated by a resistor. In this chapter, we present the equations and theories that make it possible to evaluate the uncertainty of an indirect measurement.