In approximate calculations and in general descriptions, like when we say "it's about ..... km away", the quantity is usually expressed by its order of magnitude, rounding it to the nearest power of ten to the number.
Referring to a length of 8· 10 ^-6 m we say that it is of the order of magnitude of 10 ^-5 m (the order of 10 micras), as 8 is greater than 5, and the power of ten increases by one unit.
A length of 1.2· 10³ m has an order of magnitude of 10 ³ m (the order of kilometres) .
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