From Leonardo Fibonacci to Modern Planning Poker
The Fibonacci sequence is one of the most famous mathematical sequences: 0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144... Each number is the sum of the two preceding numbers. This seemingly simple sequence hides deep mathematical principles and surprisingly appears everywhere in nature – and in Scrum Poker.
Leonardo Fibonacci (actually Leonardo da Pisa) was an Italian mathematician who lived in the 13th century and is considered one of the most important mathematicians of the Middle Ages.
In his work "Liber Abaci" (Book of Calculation), Fibonacci posed a famous problem:
"A pair of rabbits is placed in an enclosure. How many pairs will there be after one year, if each pair produces a new pair every month starting from the second month of life?"
The solution? Month 1: 1 pair, Month 2: 1 pair, Month 3: 2 pairs, Month 4: 3 pairs, Month 5: 5 pairs, Month 6: 8 pairs... the Fibonacci sequence!
The ratio of consecutive Fibonacci numbers approaches the Golden Ratio:
5 / 3 = 1.666...
8 / 5 = 1.600
13 / 8 = 1.625
21 / 13 = 1.615...
34 / 21 = 1.619...
→ Converges to φ = 1.618033988...
The Golden Ratio is considered an aesthetically perfect proportion and appears in art, architecture, and nature (e.g., nautilus shell, sunflower).
The Fibonacci sequence grows exponentially, but not linearly. The gaps between numbers become increasingly larger:
| Position | Value | Difference | Ratio |
|---|---|---|---|
| F(5) | 5 | +2 | - |
| F(6) | 8 | +3 | 1.60x |
| F(7) | 13 | +5 | 1.63x |
| F(8) | 21 | +8 | 1.62x |
| F(9) | 34 | +13 | 1.62x |
Plants
Animals & Physics
The Fibonacci scale is perfect for story point estimation because it reflects the natural uncertainty of larger tasks.
For well-understood, small tasks, we can estimate precisely. The differences between 1, 2, and 3 story points are clearly recognizable.
For complex, uncertain tasks, precise estimates are impossible. The jump from 8 to 13 signals: "Both are large, but 13 is significantly more complex." A linear scale (8, 9, 10, 11, 12, 13) would suggest false precision.
Without Fibonacci, teams debate endlessly: "Is this 16 or 17 points?" With Fibonacci: "5 or 8 points?" – The gap forces simplification: Is it more medium (5) or large (8)?
The large jump from 13 to 21 signals: "This is too big!" Teams are encouraged to break down 21-point stories into smaller, manageable pieces.
Studies show: People can estimate magnitude (small, medium, large, very large) better than exact values. Fibonacci perfectly maps these magnitudes.
While Fibonacci is the standard, some teams use alternative scales:
Adjustments: ½ for micro-tasks, 20 instead of 21 (rounder), 40 and 100 for epics.
When to use: Teams that need to estimate very small tasks (½) or very large ones (100 for epics).
Advantage: Very intuitive, no numbers (avoids time conversion).
Disadvantage: More difficult for velocity tracking (how much is "L"?).
When to use: Rough pre-estimates or teams that are absolute beginners in Agile.
Advantage: Mathematically clear, always doubles.
Disadvantage: Very large gaps (4→8→16), less nuanced.
When to use: Engineering teams that prefer binary thinking.
Advantage: Easy to understand.
Disadvantage: Suggests false precision, endless debates ("7 or 8?").
Recommendation: ❌ Not for Planning Poker – use Fibonacci!
| Card Value | Meaning | Examples |
|---|---|---|
| 0 | No work | Story already complete, only documentation needed |
| 1 | Trivial | Text change, config update |
| 2 | Very small | Small CSS styling, simple validation |
| 3 | Small | New input field with backend connection |
| 5 | Medium | API endpoint, simple CRUD operation |
| 8 | Large | Feature with multiple components, complex logic |
| 13 | Very large | Authentication system, complex feature |
| 21 | Epic (split!) | Too large for one sprint – break it down! |
| ? | Unclear | Requirements unclear, more research needed |
| ☕ | Break | Team needs a coffee break |
Start now with precise, consistent story point estimates.
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