Fibonacci Story Points
Most planning poker decks are built on the Fibonacci sequence: 1, 2, 3, 5, 8, 13 and so on, where each number is the sum of the two before it. Teams use these numbers as story points, a unit that expresses how big a piece of work is compared with other pieces of work. This guide explains why the sequence fits estimation so well and how to use it without falling into common traps.
Why Fibonacci works for estimation
The gap between numbers grows as they get larger. The difference between 1 and 2 is small, but the difference between 13 and 21 is eight points. That mirrors reality: the bigger an item is, the less precisely anyone can predict it. Choosing between 5 and 6 would be false precision, so the deck simply does not offer it. The team is forced to decide whether a story is closer to 5 or closer to 8, which is a far more useful conversation.
Relative sizing instead of hours
Story points measure effort, complexity and uncertainty together, and they only mean something relative to each other. A story worth 8 points should feel about twice as big as one worth 4. People are generally better at comparing two things than at predicting an absolute duration, and points do not change depending on who ends up doing the work. Over several sprints the teamās velocity, the number of points it finishes per sprint, turns those relative sizes into a useful planning forecast.
A practical way to start is to pick one small, well-understood story as a baseline, call it a 2 or a 3, and size everything else against it.
The modified Fibonacci sequence
Many teams use a modified sequence that rounds the large values to friendlier numbers, such as 0, 1, 2, 3, 5, 8, 13, 20, 40, 100. The exact numbers matter less than the principle: the larger the estimate, the wider the gap. Fun Fox Planning Poker uses 0, 1, 2, 3, 5, 8, 13 and 21, plus two special cards.
What 0, ? and the coffee cup mean
- 0 means the work is trivial or already done and needs no meaningful effort.
- ? means āI cannot estimate thisā. The story is unclear, and the team should ask questions or split out a research task before voting again.
- ā means āI need a breakā. It is a polite signal that the session has run long and the team should stop for a moment.
What to do with large estimates
A 13 or a 21 is a warning sign more than an estimate. Large stories hide risk and usually contain several smaller deliverables. When the team votes at the top of the scale, it is normally better to split the story and estimate the pieces than to accept a big, vague number.
Common pitfalls
- Converting points to hours. Once a point equals a fixed number of hours, you have lost the benefit of relative sizing and recreated time estimates with extra steps.
- Comparing velocity between teams. Each teamās points are calibrated to its own baseline, so totals from different teams are not comparable.
- Inflating points to look productive. Velocity is a planning tool, not a performance score. Treating it as a target encourages inflation and makes forecasts useless.
- Averaging the votes. If the team votes 3, 5 and 13, the average of 7 hides the fact that someone sees a risk the others missed. Discuss before settling.
- Re-estimating finished work. Keep the original estimate. The goal is to learn from the difference, not to make the past look accurate.
Putting it into practice
Fibonacci cards work best inside a regular planning poker session where everyone reveals their vote at the same time. If you are new to the technique, read what planning poker is first. If your team prefers coarser categories for early backlog grooming, compare this approach with T-shirt sizing.