How to specify WIP limits in Kanban

One of the things Agile tries to achieve is the concept of 'doing it trumps talking about doing it', estimating is one of these things where you spend too much time worrying about how long it'd take you to do something if you eventually got on and did it. And generally, whatever estimate you come up with, you're wrong regardless!

So scrap estimates.

Kanban can tell you the cycle time for the tasks you put through it, and you can plot them on a graph to get a distribution curve of times actually taken (ie from when the ticket was placed on the board in progress to when it was removed).

Dennis Stevens suggests t-shirt sizing your tasks to get an understanding of whether to perform the or not, but t-shirting is a 10 second task in most cases - if I ask you how big a task is, you'll be able to say "trivial", "about average" or "mhmhmhmhhh.. that's gonna cost you g'vnor". Waste about that long on this kind of process, and then get on with working those tasks. Do not try to estimate every task, just those you're concerned about.

With Kanban I think the canonical answer is this: don't bother with estimates.

For prioritisation, there is a concept in Kanban called Classes of Service that you can use for those tasks you want to alter the prioritisation for - if something is not a priority (a task that is lengthy-but-important is still important, a task that is quick-but-unimportant is still unimportant after all) you can put it in as a slow-burn or intangible task that will be done after all the higher-priority tasks are complete and someone has time to devote to the task.