Abstract: There is disclosed an internal sizing apparatus comprising a pneumatically activated probe that moves axially within a shoe and non-destructively measures the interior dimensions of the shoe. A linear pneumatic actuator is mounted between a heel piece and a probe. A linear potentiometer is mounted above the actuator and also connects to the probe. The apparatus is inserted into a shoe with the heel piece seated against the interior heel portion of the shoe. A computer system controlling the actuator extends the probe linearly into the shoe until the probe contacts the toe portion of the shoe. The potentiometer then measures the linear distance traveled by the probe and thus determines the internal linear dimension of the shoe. Depending on the type of probe, three-dimensional internal measurements of the shoe can also be quantified.