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## Estimate Orders of Magnitude

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**By using rough order-of-magnitude estimates,
you can check calculations and estimate whether tasks are even plausible
before spending time to plan them more accurately.**

An *order-of-magnitude estimate* is an
estimate to the nearest power of 10. For instance, an order-of-magnitude estimate
of 400 means the true value is closer to 400 than 40 or 4,000. The
estimates we’re discussing in this hack are called *rough order-of-magnitude* (ROM) estimates
because we’re not completely sure we’re within an order of
magnitude.

Other terms for this kind of estimate are *ballpark estimates* (as in, “Are we
even in the ballpark?”) and *educated* or *scientific
wild-ass guesses*. As all of these names suggest, the idea is
to determine roughly how large a number is, or whether a task is
trivial, possible, or absurd.