Story points

Story points are relative units of effort used to estimate the time a team requires to implement a user story. Effort can be defined as "the number of labor units required to complete a schedule activity ..." and requires the consideration of complexity, risk and uncertainty. The use of story points has a growing body of evidence to suggest that they are quicker to use and provide more accurate estimation than objective units such as hours or days.

A team estimates story points by first identifying a 'baseline' user story that each member can relate to and assigning it a number of story points: the quantity of effort (time) this story would take each team member will differ. The remaining user stories are then assigned story points relative to the baseline story. Planning poker using a modified Fibonacci sequence is a common technique for this activity. Story points are highly specific and their objective value will differ between teams and between the members of a team.

Example: A team consists of members A (very experienced), B (experienced) and C (less experienced). At a planning poker session they assign story points to the user stories in their backlog. They agree to use user story X as their baseline and assign it 5 user points;

• A estimates it would take him/her about 30 minutes: 1 story point for A is about 5 minutes.
• B estimates it would take him/her about 60 minutes: 1 story point for B is about 10 minutes.
• C estimates it would take him/her about 5 hours: 1 story point for C is about 1 hour.

Relative to X and its value of 5 user points, the team members go through the rest of the user stories and assign story points. The team decide to do week long sprints where they each work 20 hours. During sprint planning they consider the number of story points they can manage;

• A estimates he/she can do about 240 story points in a week
• B estimates he/she can do about 120 story points in a week
• C estimates he/she can do about 20 story points in a week