Fibonacci vs Linear Estimation Scales
Compare Fibonacci and linear estimation scales for story points. Learn when each is appropriate and how the growing gaps in Fibonacci prevent false precision.
Detailed Explanation
Fibonacci vs Linear Scales
Choosing an estimation scale affects how teams think about and discuss effort. The two most common options are the Fibonacci sequence and linear (1-10) scales.
Fibonacci: 1, 2, 3, 5, 8, 13, 21
The Fibonacci sequence increases non-linearly. The gap between 1 and 2 is just 1, but the gap between 13 and 21 is 8. This mirrors reality: the bigger a task is, the less precisely we can estimate it.
Linear: 1 2 3 4 5 6 7 8 9 10
Fibonacci: 1 2 3 5 8 13 21
Advantages:
- Forces the team to round up or down, preventing debates about whether something is a 6 or a 7.
- Large items (13, 21) signal that the story should probably be split.
- The natural breakpoints match human cognitive perception of "small, medium, large."
Linear: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10
A uniform scale where every increment is 1.
Advantages:
- Simple to understand.
- Fine-grained for teams that want more precision on smaller items.
Disadvantages:
- Teams waste time debating 6 vs 7 -- a distinction that rarely matters.
- Gives false confidence in the precision of large estimates.
- Does not naturally signal when a story is too large.
Which Should You Use?
| Scenario | Recommended Scale |
|---|---|
| New to estimation | Fibonacci |
| Mature team wanting simplicity | Fibonacci |
| High-level roadmap sizing | T-Shirt (XS-XXL) |
| Small, well-understood items | Linear is OK |
| Mix of small and large items | Fibonacci |
Most agile coaches recommend Fibonacci because it balances simplicity with cognitive accuracy.
Use Case
Reference this comparison when your team is debating which estimation scale to adopt, or when transitioning from hours to story points.