Physics learning cannot be separated from the existence of physics measuring instruments, but their existence in schools are very limited. Therefore, creativity and innovation are needed to develop physics measuring instruments that are easily accessible by schools. This research aims to design and construct a liquid density measuring instrument by applying Hooke's law and hydrostatic pressure. The method used in this research is a quantitative descriptive method with the stages of designing, constructing, developing, and testing the measuring instrument. The design and construction of the measuring instrument in this study is carried out using tools and materials that are simple and easily obtained, such as a glass pipe, PVC pipe, rulers, springs, and wooden table. The liquids used to test the instrument are cooking oil, lubricant, and water. The measurement results of the liquid density using the measuring instrument are in accordance to the known value or the standard.