In recent years, agile methods of software development have gained a lot of attention in the field of software engineering. Several estimation techniques have been proposed by several authors and developers in recent years. This paper performs a Systematic Literature Review aiming to identify the most used metrics e/or methods in the development of agile software and the most used size metrics regarding effort estimates, deadlines and costs in a planning of agile software project. The results suggest that Planning Poker is the most popular technique for agile teams in the planning phase, Story Point and Point of Function are the most used metrics in agile projects for estimating size, time, effort, productivity and cost.