Software reliability is an important aspect in software engineering enviourment. Software reliability is introduced as failure free operation in specified enviourment. Various studies show that the software reliability is defined in three categories that are improvement, modelling and measurement. In this paper, we will study the reliability metrics to improve the software reliability. Reliability metrics are used to measure software reliability. Metrics are unit of measure for the software reliability, which are used to measure the reliability of software product. This paper contains the review of appropriate metrics to improve the reliability. The most commonly used reliability metrics is MTTF (mean time to failure).