What Is a Burn down Chart? - All the Parts Explained in Detail
What Exactly Are Burn down Charts and What Are They Used For? - a Definition
What is the definition of a burn down chart?
A burn down chart is a visual tool to track progress in agile project management. It is most commonly used in Scrum teams to inspect the progress on a sprint backlog. In general, it can be used to track progress against any numeric goal against time.
The most prominent variation of a burn down chart is the burn up chart. Burn up charts are commonly used to track releases in software development.
What parts is a burn down chart made of?
Burn down charts are made up of the following components:
1. The horizontal axis
This axis tracks the time passing while the work is being done. In the case of a sprint this axis would list all the dates included in the sprint.
2. The vertical axis
This axis tracks the work left to complete. As work is being completed, the work left to complete becomes less. It could thus also be said that this axis tracks the inverse of the progress being made.
3. Start point
The sum total of the work to be done. When making progress over time the amount of work becomes less, but it always starts at the start point.
4. Finish point
The finish point represents the end of the time interval tracked by the chart. The finish point represents the point in time where the amount of work marked by the start point is estimated to be completed by.
In Scrum the time interval is a sprint. In this case the burn down can also be called a sprint burn down chart.
5. Ideal line
This line marks the ideal way that work would be completed throughout the time interval to meet the finish point at the end of the time interval.
As the name suggests this is only an ideal and serves as a guideline. In fact, it is usually physically impossible to follow the line exactly because work gets completed in chunks. Imagine that in software development you are developing a new feature: You could only say that the feature is complete when it is fully implemented, integrated and tested. You wouldn't write a line of code and then call that line of code complete.
For sprint burn down charts in Scrum the ideal line serves as a guideline to complete the full sprint backlog and reach the sprint goal by the end of the sprint.
6. Actual line
The actual line is where the work done is marked as completed. As work on a project or sprint is being done, the line will go down and give an indication if the project or sprint is on track to be completed by the finish point.
As mentioned above, the ideal line serves as a guideline. The closer the actual line runs to the ideal line, the more confidence can usually be had that the project or sprint is on track.
So what exactly does the vertical axis of a burn down chart track?
The vertical axis tracks the work to be done. By the nature of this it must be an abstract unit. In theory it can be any measure that represents a numeric goal.
For sprint backlogs in Scrum story points are most commonly used. Story points are an abstract point system to estimate the complexity of pieces of work in relation to each other.
In the case of story points the start point of the burn down chart is the sum total of the estimates of the sprint backlog. Other measures to be used the vertical axis of the chart could be hours or developer days.
What else can burn down charts be used for?
Besides using them in agile project management, burn down charts can be used to track any numeric goal. This means that any project can be tracked using a burn down chart, e.g. personal goals like a number of books to read or saving a certain amount of money over a period of time.