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Agile Tip #3 – Story Point Scales

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Tip #3:  Choose a meaningful story points scale for estimating user stories.

The MSF Agile 5.0 template uses story points as the estimation unit for items on the product backlog (User Stories).  The field itself is a double and supports different number formats, however teams that use story points successfully agree upfront on a scale that they apply across all stories on their backlog. 

imageBefore choosing a scale for your team, it’s important to be comfortable with what story points are.  Story points are simply an abstract unit of size (or complexity) assigned to each story on your backlog.  They’re not hours, days, weeks, or any other scale that has an absolute measurement.  They’re simply “points”.  I recommend walking through Mike Cohn’s presentation on Agile Estimating and Planning that goes into specifics on story points and how to use them.  They three key advantages he lays out in his presentation are:

  1. Story points force the use of relative estimating
  2. Story points focus on size, not duration
  3. Story points put estimates in units that we can add together

In short, story points provide a relative size for each story on your product backlog that can be used to plan iterations and determine the team’s velocity (amount of work planned or completed in an iteration). 

The Fibonacci sequence (1, 2, 3, 5, 8, 13, etc) seems to be the most popular scale being used by Agile teams.  It’s well known, non-linear, and provides nicely sized “buckets” that people are comfortable using.   Whatever scale your team chooses, be sure that everyone on the team understands it and is committed to using it – you’ll find success with story points easier to come by when your agree on the scale up front.

Comments

  • Anonymous
    April 22, 2010
    At SSW we use t-shirt sizes as a way to stop the develoeprs thinking of the number as hours.
  • Anonymous
    April 23, 2010
    I've used t-shirt sizes as well and agree that they REALLY help avoiding the hours conversation.  The downside IMHO is that you can't add them together to determine total size.  How do you determine velocity with t-shirt sizes?
  • Anonymous
    September 06, 2011
    @Aaron: errSmall = 1Medium = 2Large = 3XL = 5XXL = 8XXXL = 13