Order of magnitude

I have a little bit of difficulty with this formula here,

If order of magnitude spread is -50% to +50%

And the actual cost of project is $100,000
Then 50% of it is $50,000

So the range will be $50,000 to $150,000,


However on some prep material that I have found, a project with target price of $100,000, has a range of  $75,000 - $175,000 with this level of estimation. Is this because anything higher than %50 i.e. 75% is also considered rough order of magnitude?

Please help me understand this.

By the way I think I found a typo in my prep book , on page 169 of "The PMP Exam, how to pass on your first try, Andy Crowe", it says the order of magnitude estimate ranges from -50% to +100%, do you think that's a typo or am I missing something?


Yes you are right.  Order of magnitude, in every book it differs.  As per PMBOK v 4, it is mentioned 50% (+ or -) and we should go by PMBOK.

Also, it is mentioned that definite magniture is 10% (+ or -) and budgted not mentioned. In some other book it is mentioned that -10% to 25%.

If anyone is having different openion, please let me know. Thanks




I don’t know the answer, I am also in the search for the australianwritings answer. But I am sure somebody will definitely know the answer. So I would request to everyone here that who know the answer to this question please explain it.

I've studied your post of "order of magnitude" formula it was quite interesting and enthralling to read thank you Godaddy 99 Rs Domain Name even I needed it and searching on the internet