order of magnitude

In a ratio scale based on powers of ten, the order of magnitude is a measure of the nearness of two figures. Two numbers are "within an order of magnitude" of each other if the ratio of the greater to the lesser is between 1 and 10. In other words, the two numbers are within about a factor of 10 of each other.

For example, 1 and 1.02 are within an order of magnitude, as well as 1 and 2, 1 and 9, and 1 and 0.2. However, 1 and 15 are not within an order of magnitude, since their ratio is 15/1 = 15 > 10. The reciprocal ratio, 1/15, is less than 0.1, so the same result is obtained.