What is an order-of-magnitude estimate?

Answer 1

It is a bit confusing. An order of magnitude is a factor of 10, but an order of magnitude estimate is more like a factor of 3, or the square root of 10. In some cases it is simply a "ball park" estimate. For example if a company give an order of magnitude estimate for a major construction project of 10,000,000 dollars, it could be anywhere from 3 million to 30 million, but usually it means roughly 10,000,000, give or take a few million.

Answer 2

It is a rough estimate, which aims to tell you the approximate order of magnitude, so basically, the closest power of ten.