Story point
What a story point measures
A story point does not measure the time needed to complete a story. It captures a combination of factors that influence perceived effort:
- Complexity: how difficult the technical implementation is.
- Effort: the amount of work required.
- Uncertainty: what the team does not yet know about how to approach it.
Each team defines its own story point scale. A 3-point story in one team does not mean the same thing as a 3-point story in another team.
How It Works in Practice
Story point estimation works by relative comparison:
- The team selects a reference story of well-known size and assigns it a base value (for example, 2 points).
- The remaining stories are estimated by comparing them with that reference: is this story twice as big? → 4 points. Half as big? → 1 point.
- The most common scale is the Fibonacci sequence (1, 2, 3, 5, 8, 13, 21) because its increasing gaps reflect the uncertainty inherent in large estimates.
The sum of points completed in a sprint is the team's velocity, which serves as a reference for estimating how much work the team can take on in future sprints.
Story point vs. ideal time
A common confusion is to equate the story point with the "ideal workday." Although some teams calibrate their story point against a time reference, the two concepts are different:
- Ideal time is the unit of effort under conditions of full concentration, without interruptions. It is used to estimate tasks within the sprint.
- The story point is a relative unit of size, used to estimate stories in the Product Backlog. It does not imply any specific amount of time.
A story point may represent four ideal hours on one team and a whole day on another. What matters is that the scale remains consistent within the same team over time.
Limitations
- Story points are not comparable across teams.
- If they are used to measure productivity or compare teams, teams tend to inflate their estimates.
- With generative AI tools that speed up parts of the work, historical velocity can quickly become outdated.
Common mistake
Comparing velocities across different teams. "Our team does 40 points per sprint and the other one does 80" says nothing about the relative productivity of the two teams: each has defined its point differently. Using story points to compare teams or to pressure one team to match another's velocity destroys the honesty of the estimates and degrades the metric until it becomes useless.
Resources
🎙️ Ep. 1: Serie Fibonacci y estimación ágil [Fibonacci Sequence and Agile Estimation]Scrum Manager Podcast · Spotify · In Spanish
🎙️ Ep. 10: Estimar o no estimar [To Estimate or Not to Estimate]Scrum Manager Podcast · Spotify · In Spanish
See also
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