Product owners and managers always want dates or the number of days work will take to be completed. The problem is that WE developers cannot say for sure, but what we can agree on is how big a problem actually is.
Many companies and developers have come up with different ways to calculate the size of a user story from using numbers to T-shirt sizes. The Agile methodology uses a system known as Planning poker.
Planning Poker, involves the team taking a user story with agreed acceptance criteria, discussing it and showing a number from the Fibonacci sequence on a card.
The sequence usually used is 1, 2, 3, 5, 8, 13, 20….
It is recommended that User Stories deemed larger than 8 should be split across multiple user stories.