I’m not sure I know. If you do, please tell me.
I have however, observed backlogs both large and small being well managed according to what Scrum says about the Product Backlog. The following are bits of the Scrum guide that speak about the Product Backlog (some paraphrasing):
- It is an ordered list of everything that might be needed in the product
- It is the single source of requirements for any changes to be made to the product
- It is never complete; it evolves as the product evolves
- It contains items, each with the attributes of description, order, estimate, and value
- It grows into an exhaustive list as the product is used, gains value, and as the market provides feedback
- Refinement should not require more than 10% of the Development Team’s capacity
- At any point in time, the work remaining to reach a goal can be summed
These things being said, it’s still not quite clear how big one should be. The guide doesn’t exactly spell out a number of Product Backlog Items or a size in MB or the time it would take Morgan Freeman to record the audio book version.
I do feel I can say a Product Backlog is too big if:
- It contains items that are not needed in the product (from point 1)
- Refinement requires more than 10% of the Development Team’s capacity (from point 6)
Simple, yet difficult to master.
As with most things in the Scrum guide, the particulars are left for self-organizing teams to discover, decide upon then establish.