At the hardest grum is the sprint. Sprints are short time boxes during which the team turns product backlog items into working product. That is, they take an idea and implement it. All of your sprints should be of the same length. Any length you choose is fine, up to a month. You don't want to do six weeks or two month sprits. It's just too long. Nearly all teams choose a sprint length that is a multiple of weeks. One week, two weeks, three weeks for four weeks You won't find a lot of teams choosing to do three-day sprints. That just makes it too hard to feel the rhythm of a sprint. And that rhythm is important. You want a team to get into a regular rhythm. If they're doing one-week sprint, for example, after a while they don't even think about it. They come into the office on Monday knowing that is Sprint Planning Day and that Friday will be for review, retrospective, and releasing the product. The same idea applies with two, three, or four-week sprints. The sense of rhythm is important. This means you don't want to change your sprint lengths all the time. When I first started doing Scrum, we started each planning meeting by deciding how long that sprint would be. We'd do a short sprint, two weeks, if we were working on small stuff that could be finished in that amount of time. we'd a long sprint if felt the need for a LONG time to complete the work of the new sprint. Even did a few six-week sprints back then. We learned, of course, that six weeks was too long. But we also learned that changing lengths was a bad idea. We do a four-week sprint, then a two, and then another two. Then a three, a six, two and so on. we never got a sense of rhythm to our work until we settled on one length. This doesn't mean that whatever length you pick becomes a life sentence. When I say you shouldn't change sprint lengths, I mean don't bounce back and forth. Pick a length and stick with it until you feel like you have a good reason to make a change. You can change Sprint lengths but don' bounce around between different lengths.