Density measurements were performed on several nanofluids containing nanoscale particles of aluminum oxide (Al2O3), zinc oxide (ZnO), copper oxide (CuO), titanium oxide (TiO2), and silicon dioxide (SiO2). These particles were individually dispersed in a base fluid of 60:40 propylene glycol and water (PG/W) by volume. Additionally, carbon nanotubes (CNTs) dispersed in de-ionized water (DI) was also tested. Initially, a benchmark test was performed on the density of the base fluid in the temperature range of 0–90 °C. The measured data agreed within a maximum error of 1.6% with the values presented in the handbook of American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE). After this validation run, the density measurements of various nanofluids with nanoparticle volumetric concentrations from 0 to 6% and nanoparticle sizes ranging from 10 to 76 nm were performed. The temperature range of the measurements was from 0 to 90 °C. These results were compared with the values predicted by a currently acceptable theoretical equation for nanofluids. The experimental results showed good agreement with the theoretical equation with a maximum deviation of for copper oxide nanofluid and average deviation of for all the nanofluids tested.