Assessment of quality of object oriented software during design phase has been a prime objective among researchers in software engineering discipline. There are many available tools that offer the software product quality from its code. Unfortunately, assessment of design quality has been more of a theoretical issue and the software engineering market lacks readily available tools for this purpose. We make use of a set of UML diagrams created during the design phase of the development process to calculate design quality. UMLet software has been used for creating the UML diagrams. Design metrics are fetched from the UML diagrams using a parser developed by us and design quality is assessed using a hierarchical model of software design quality. To validate the design quality, we compute the product quality from software code that corresponds to the UML design diagrams using available tools METRIC 1.3.6, JHAWK and Team In a Box. The objective is to establish a correspondence between design quality and product quality of object oriented software and thus identifying the design metrics that play decisive role in the quality of a software product. For this purpose, we have chosen seven software of known quality as low, medium and high. A strong correlation has been observed among the results obtained from the two approaches i.e., between design quality and the product quality, which validates our chosen metrics set for determining software design quality.