Order of magnitude

The phrase order of magnitude is sometimes used (often in the plural) loosely to mean 'a lot' - "he is bigger than me, by several orders of magnitude." The use of the phrase is perhaps felt to give an air of impressive scientific authority, or to draw on the strength of the impressions of enormous size that modern science gives.

The problem is that the term order of magnitude has a precise meaning. The casual speaker probably misunderstands it completely. In academic writing, only use the phrase in its proper meaning. Properly, order of magnitude means, in our mathematics based on the decimal system of numbers, "an increased (integral) power of ten". Less mathematically stated, "the column into which you put the digit of a figure". A hundred, for example, is an order of magnitude bigger than ten, and an order of magnitude smaller than a thousand.

OED defines it, very carefully, as "approximate number or magnitude in a scale in which equal steps correspond to a fixed multiplying factor (usu. taken as 10); a range between one power of 10 and the next."

When speaking in a University context, or writing academic papers, only use order of magnitude in its mathematically correct sense.