Backlog item effort

On Scrum framework, some practitioners estimate the effort of product backlog items in ideal engineering days, but many people prefer less concrete-sounding backlog effort estimation units. Alternative units might include story points, function points, or “t-shirt sizes” (1 for small, 2 for medium, etc.). The advantage of vaguer units is they’re explicit about the distinction that product backlog item effort estimates are not estimates of duration.  Also, estimates at this level are rough guesses that should never be confused with actual working hours. Note that sprint tasks are distinct from product backlog items and task effort remaining is always estimated in hours.