What are Story Points? Understanding Story Points for Agile Estimation & Planning

What are Story Points?

Story points are a unitless measure teams use in Agile project management to estimate the effort required to complete a task. Teams assign a story point value to user stories based on relative complexity, size, and risk. For who on the team does the estimating, see should the Product Owner estimate story points?

Before clarifing what we mean by relative and unitless, let's take two examples to understand how estimating with story points works:

User story A, estimated as one story point, will roughly take the same effort as User story B, also estimated as one story point.

User story X, estimated as three-story points will take roughly three times the effort and time as User story A estimated as one story point

'A relative estimate'—what does that mean?

When teams estimate a story, they compare the effort relative to other stories they have already estimated. Think of it like using a fruit estimation scale:

• 🍓 Strawberry: Represents a small story with minimal effort.
• 🍏 Apple: Represents a medium-sized story with a moderate amount of effort.
• 🍉 Watermelon: Represents a large story that requires even more effort

Let's estimate the size of a cherry 🍒 relative to the fruits on this scale. Any team comparing the cherry and other items on the scale can quickly see it falls into the same category as the strawberry. It's quick and easy because the differences between the weights of the items on the scale are apparent.

This is why the story point scale uses the Fibonacci sequence, or a close approximation, rather than all numbers between 0 and 100:

So with relative estimation you are always comparing the item you want to estimate, the cherry 🍒 in this case, with other items you have already estimated and asking if it is the same size as the strawberry 🍓, the apple 🍏 or watermelon 🍉?

'A unitless scale', what does that mean?

Unlike the meter scale, where 1 meter is defined as one ten-millionth the distance from the equator to the North Pole, a unitless scale does not correspond to a fixed, universally defined quantity. 

This means:

one story point for one team is likely not the same as one story point for other teams.

So if someone is trying to compare teams based on story points completed per sprint, then feel free to share this article 😉

How do story points translate to time?

We still need to answer how story points translate to time. In the next post, What is agile velocity, we will answer this question by introducing the concept of velocity.