Education and learning is one of the world's largest markets for internet applications. Learning and training at work is probably the fastest growing sector. Before measuring the usability of these e-learning applications, users have to face unknown risks of failure of applications. This paper represents five metrics to measure the usability of E-Learning systems through user interface. These metrics are: Time of user feedback, average of using help methods, average of using undo, average time spent in any page, and average of using e-learning system's search engine. We focused to measure the using of e-systems rather than the content of the systems. These metrics cover the three parts of usability (ease of use, ease to learning, and task matching). In addition, these metrics satisfy the definition of usability for both human computer interaction and software engineering.