Sorry for posting this late, but I have done this as part of an existential risk meetup in San Francisco.

We experimented quite a bit, but here is one general algorithm for making fermi estimates as a group.

• State the question (how many almonds are in that bag) and what people are allowed to see/measure (you can look at the bag, inspect it, can not touch).
• Ask everyone to give their immediate intuitive 90% confidence interval. This in itself is essentially the smallest possible fermi estimate.
• Give people around 2 minutes to sketch out something, and then give new estimates.
• Spend another 8-15 minutes for a longer, more mathematical answer. Allow people to use calculators, spend some time writing out thoughts.
• Go around the room, asking for estimates and the methods used to come up with them.
• Try to collectively decide on one model. Have everyone give their inputs to that model. See if you can come up with an answer with higher certainty than any person could come up with individually.
• Look at all of the results again, with the actual result (if possible). Compare & contrast.

General Recommendations

• Use confidence intervals! As mentioned above, if you can do this, you will get much more interesting answers.
• Try to graph out your models. I made an example here of a few ways to do this.
• Compare answers and see if the group can come up with a consensus to first a best model, or second the actual number.
• Consider what would help make a fermi question calculator program :) (I'm starting making one, having a difficult UI time)

Also, if together you guys hear of any good books or new methods for doing large Fermi estimates, please post.