Reynolds number for an object moving at a speed *V* through a fluid with density *ρ* and viscosity *μ* is defined as

where *L* is a representative scale of the object (the object length, for example). According to Reynolds Number Scaling in an incompressible (constant *ρ*) fluid, *C _{D}* is the same for two identically shaped objects if the Reynolds number is the same for the two objects. This is true even if the two objects are in different fluids. For example, a large object in a very viscous fluid (high