How many spaces to open in Open Space?

A helpful conversation on the Open Space Technology list about how many breakout spaces to prepare (answer is from Chris Corrigan).

In groups of up to 50 I usually prepare breakout space enough for half of those people to host topics over the course of the event.  Therefore a group of 40 needs 20 breakout spaces.  Spread over two timeslots, that means 10 breakout spaces.  Spread over three timeslots, well why not?  Still 10 spaces.  You can never have too much space. (An update from Chris: good rule of thumb is to take the number of people and divide by 10 for how many sessions per timeslot – sparked by a conversation that 8 felt too small for a group of 100.)

For groups 50-100 I assume something like 30 sessions will be held.  For group of 100-200, up to 50 sessions will be held.  200-500, perhaps 80.  Groups bigger than 500 can generate sessions at a rate of 15% of the total number of people:  600 will produce up to 90, 800 might produce 120 and so on.

So a formula… 0-50 = 50%, 50-100 = 30%, 100-200 = 25%, 200-500 = 20%, 600+ = 15%


And this from Lisa Heft: for smaller groups such as 10 or 40, estimate discussion groups of 5 to 7 people. For groups over 40, estimate discussion groups of 10 to 15. And always have a few in your back pocket.

Thank you to the learners and teachers on the list for this handy guide. I’m always hunting for it as numbers are just not something that stay in my head.