The Sprint length in Scrum is 30 days or less. Most teams work with 2 or 3 week Sprints and the most common recommendation for the Sprint length seems to be 2 weeks. 30 day Sprints seem to be very rare.
The general thinking here is that shorter Sprints lead to more frequent inspect&adapt regarding the product (Sprint Review) and the process (Sprint Retrospective). When a team is capable of doing 3 week Sprints it should therefore try to work with 2 week Sprints and then 1 week Sprints.
But I think there is missing an important aspect: When the team is capable of delivering within a certain Sprint length there are actually two possibilities for further improvement:
- Shorten the Sprint length to reduce feedback cycles and allow more frequent inspect&adapt.
- Deepen the teams capability by reducing the Definition of Ready (start the Sprint with a less formal specification) or increasing the Definition of Done (e.g. by including live deployment).
Which direction to take is – of course – dependent on the specific context.
Shorten the Sprint length is valuable if
- the Product Owner is actually able to react that fast to feedback about the product
- the team is able to create and implement process improvements that fast
Deepen the teams capabilities by reducing the Definition of Ready is valuable if
- cross-functional work seems valuable not only for the implementation but also for the definition of the „what“ (remember the benefits of cross-functional work: more creativity, higher quality)
- the Product Owner is overloaded (e.g. he is a Jeff type of Product Owner but is forced to work like a Walter or Marty)
Deepen the teams capabilities by increasing the Definition of Done is valuable if
- the product increment isn’t really shippable until now (e.g. integration tests are missing; the demo is done in a branch)
- there are often problems in the downstream processes (e.g. operations has problems with deploying the product increment into production)
- When your team becomes more capable you should discuss if you want to shorten the Sprint length or deepen the capabilities of the team.
- When your team is capable of doing the current Sprint length but not a shorter one, you should discuss if it would be valuable to extend the Sprint length and deepen the capabilities of the team.