A density calibration of homogeneous polymeric materials in the range of 0.9 to 2.2 g/cm3 with micro Computed Tomography (CT) scanning was devised and its accuracy, repeatability and potential sources of error were investigated. The density of unknown materials could be determined successfully in many cases with this calibration. However, in some cases the experimental values deviated significantly from the actual values. These deviations could be attributed mainly to chemical compositional differences compared to the calibration materials. Dual energy CT could be used to determine whether a material is within the range of atomic composition of the calibration materials, in which case the calibration function is accurate. If a material is outside the chemical composition range determined by dual energy CT, the calibration is not applicable and accurate density cannot be determined.