The present invention provides a calculation device, calculation method, and calculation program with which the length of a target region required for a body model can be determined by means of a simple operation. This calculation device 1 configures a wearable device to start measurement of a region to be measured (S101). After starting measurement of the region to be measured, a worker wearing the wearable device performs an operation such as rotation of an arm, for example. The calculation device 1 acquires measurement information multiple times (S102) in a chronological manner and calculates a body model on the basis of the acquired measurement information (S103-S105). During calculation of the body model, calculation is performed to determine the length of the region to be calculated by approximately determining, using a mathematical method such as the least-squares method on the basis of the plurality of pieces of measurement information acquired chronologically, a circle or sphere having the length from the center of rotation to the region to be calculated as the radius. Then, the calculation device 1 records the calculated body model in a body model recording unit (S107).
