When we begin to estimate a user story once it has been reviewed we can estimate with Story Points. Story Points are a simple unit of measure for a software development team. They are completely arbitrary and will definitely vary from team to team. Story points are not correlated to hours of completion. The points are an abstract measure of the complexity of the user story.
Story points are sometimes measured in the fibonacci sequence of 1,2,3,5,8,13,21,34,45… Some will measure in t-shirt sizes S, M, L, and XL. I have even heard of interesting ideas of using dog breeds as a sizing measure. To get things started you would discuss with the team a baseline user story of perhaps just making a small change. Then talk through what each team member thinks the estimate should be and try to come to a consensus. It is important to point out again that given two different teams they will come to different story point totals.
We estimate user stories in our product backlog to look at the complexity of a user story. This also helps the product owner compare different user stories as they prioritize items for an upcoming sprint. Also as a team goes through a few sprints and gets a consistent cadence we can use the story points to help estimate how much work can be completed in a time period.
When you are estimating a user story in a product backlog you will see great differences in each person’s estimate. This will lead to good discussion on why someone might have a one and somebody else has an eight. Trends will emerge as you work with your team and you will learn people’s approaches and personality.