Usability quality attribute is one of the important quality attributes because it is a basic need for end-user stakeholder. Usability provides the ease of use and learnability to end user. Usability is very useful quality attribute of software architecture and architect should remember about usability aspect. Usability aspect means such type of software architecture which provides the learnability, memorability and performance. In this paper we discuss software architecture design based on usability aspect. Usability is necessary for end-users and business stakeholders. We measure and evaluate the usability through one of the mathematical equations. For the selection of usability aspect, or to evaluate the highest usability score in different architecture designs, we have taken the questionnaire from technical persons on the basis of nonfunctional requirements or sub-characteristics of usability quality attributes such as learnability, memorability and performance. Then finally we calculate the usability score.