The mysterious unit of measurement in agile. Not an hour, not a day, not a kilogram… and yet everyone talks about it.
A simple definition
A story point is an abstract unit of measurement used to evaluate the relative effort required to deliver a user story. The keyword is "relative": we don't measure duration, we compare sizes.
If story A is worth 2 points and story B is worth 4 points, that means B is roughly twice as complex as A, not that it will take twice as long.
What a story point actually measures
A story point combines three factors:
- Complexity: how technically difficult is it?
- Volume: how much work is involved?
- Uncertainty: how well do we understand the topic?
Why not hours?
Hours vary from one person to another. A senior developer and a junior don't work at the same pace. Story points let the team estimate collectively, independently of individual skill levels.
Velocity is the average number of story points the team completes per sprint. It is this indicator, not hours, that drives agile planning.
A shared reference
For story points to mean anything, the team must agree on a reference story. For example: "That login ticket we did last month is a 3. We compare everything against it."
