Why Stories in Agile have fibonacci series as estimates?

Question

All the estimates of sprint stories have estimates in fibonacci order. e. g stories with 1,2,3,5,8,13 story points. Whats the reason?

Answer 1

first of all, not always it happens, some team choose plain numbers for story points or sizes like XS, S, M, L, XL. The fibonacci series is chosen usually if you want to promote discussion about the meaning of the story. It creates on purpose a gap between the sizes so that if two developers select different sizes they need to discuss about why so much difference between the two estimations. Also, it promote to break down the story in smaller one for the big stories. Not exact science, of course, but a way to promote a common understanding of the stories.

Hope it helps.

Answer 2

One of the characteristics of the Fibonacci series is that the gaps between the values increases with their size.

When we use the Fibonacci series in estimating these gaps represent increasing uncertainty as user stories get larger.

For example, it is more difficult to estimate accurately a 13 point story than it is to estimate a 2 point story.