Story points are a unit of measure for expressing the overall effort required to fully implement a product backlog item or user story. Unlike time-based estimates, story points represent relative complexity, risk, and effort.
Key characteristics:
1. Relative, not absolute - Stories are compared to each other, not estimated in hours
2. Team-specific - A 5-point story for one team may differ from another's
3. Include all work - Development, testing, documentation, etc.
4. Account for uncertainty - More complex items get higher points
Common scales:
- Fibonacci sequence (1, 2, 3, 5, 8, 13, 21, 34...)
- Modified Fibonacci (1, 2, 3, 5, 8, 13, 20, 40, 100)
- T-shirt sizes (XS, S, M, L, XL) mapped to numbers
- Powers of 2 (1, 2, 4, 8, 16, 32)
Why Fibonacci? The gaps between numbers increase, reflecting that larger items have more uncertainty. You can distinguish 3 from 5, but not 21 from 22.
Estimation techniques:
1. Planning Poker - Team members privately select cards, then reveal and discuss
2. Affinity Estimation - Group similar items, then assign points to groups
3. Reference Story - Compare new stories to a well-understood reference
Benefits of story points:
- Faster than detailed hour estimates
- Encourage team discussion about complexity
- Reduce anchoring to 'ideal hours'
- Enable velocity tracking for planning
- Focus on relative sizing over precision
Common pitfalls:
- Converting points to hours (defeats the purpose)
- Comparing velocity between teams
- Using for performance evaluation
- Over-precision (debating 5 vs 6)
Story points feed into velocity calculations, enabling better sprint planning and release forecasting over time.