Estimate measurements by choosing an appropriate customary or metric unit, using familiar benchmarks, and judging a reasonable magnitude for length, area, volume, mass, capacity, or time. The understanding includes matching the precision of an estimate to the context, distinguishing estimates from exact measurements, and recognizing that changing units changes the numerical value but not the quantity; formal error bounds, statistical estimation, and highly precise scientific measurement are beyond this scope.
An estimate is a reasonable measurement found by comparing an object with a familiar benchmark. It is not the exact measurement, so choose a unit and level of precision that fit the situation.
Example: Estimate the length of a classroom table.
Choose a useful unit.
A table is several feet long, so feet are more useful than inches. Saying “about 4 feet” is easier than saying “about 48 inches.”
Use a familiar benchmark.
Imagine a ruler that is 1 foot long. Compare the ruler with the table. The table looks about as long as four 1-foot rulers placed end to end.
Make the estimate.
Therefore, the table’s length is approximately
The estimate is not claiming that the table is exactly 4 feet long. An exact measurement might be feet inches. Also, changing units changes the number, not the length: feet is the same quantity as inches.
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