Estimating length involves choosing an appropriate customary or metric unit, using familiar benchmarks such as an inch, foot, yard, centimeter, or meter, and reasoning about how many units compose an object’s length before exact measurement. An estimate is stated with a suitable unit and judged for reasonableness through comparison, without requiring exact conversions among units, fractional-unit precision, or formal error bounds.
To estimate a length, choose a unit that fits the object, compare the object with a familiar benchmark, and decide about how many units long it is.
Example: Estimate the length of a classroom desk.
Choose a unit.
A desk is too long to measure well with inches, so use feet.
Think of a benchmark.
A foot is about the length of a ruler or the distance from your elbow to your hand.
Imagine placing 1-foot lengths along the desk.
The desk looks about as long as four 1-foot lengths.
State the estimate with a unit.
The desk is about feet long.
Check if it makes sense.
A desk should be a few feet long, so feet is a reasonable estimate.
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