That said, I'll offer some general guidelines that can be modified to suit your current situation.
We have found that establishing an appropriate backlog is critical. When teams have too little work in the backlog, they run the risk of sitting idle when an agile story is blocked or impeded. That wastes time and money. On the other hand, when teams have extensive backlogs with excessive detail, the business runs the risk of having over-invested in plans that inevitably will change. That also wastes time and money, so we need to find a middle ground.
A healthy backlog typically includes stories at various levels of refinement. I recommend that your backlog include some ready stories at the front of the line, as well as some in-refinement stories that are further out. Ready stories have been fleshed out with enough detail that a team could work on them immediately. In-refinement stories usually aren't fully developed but are directionally correct.
For many clients that are midway through the agile transformation process, I often recommended that their teams strive for a backlog that includes one to two iterations of ready stories and one to two iterations of in-refinement stories.
For organizations that are operating at scale (i.e., SAFe), I typically look for one rolling product increment (PI) of features, sized with a reasonable level of detail for slotting purposes. For example, if you operate on a 12-week PI and are 6 weeks into it, you should have enough features defined for the remainder of the PI and half of the following PI.
The "right" level of intent for a specific team's backlog is a sliding measurement driven by variables such as velocity, volatility and the stability of the specific team and business area in question. While that is an "ideal" answer, it makes sense to establish agreement on a rough rule of thumb, with all parties collaborating where flexibility is needed.
In summary, for organizations midway through the agile transformation, the backlog might include:
- 1-2 iterations of ready work (stories on deck)
- 1-2 iterations of in-refinement work (stories being developed)
- 1 rolling PI of features in the grooming process, sized with a reasonable level of detail (slotting)
Have questions? I am happy to speak with you about your organization's needs and what a healthy backlog might look like in the context of your requirements, agile maturity level and environment. I have yet to find a one-size-fits-all model, and the best solution for your organization will not only be unique, but will also change as you continue to walk your agile path.