Estimate

An estimate is appropriate when an exact measurement is unnecessary or impossible—for example, when a structure has an irregular edge, the boundary is blurred, part of it is hidden, or the task asks only which structure is larger. Estimation is also helpful for checking whether a calculated answer is sensible.

An estimate is not an unsupported guess. It uses known information, a suitable model and clearly stated assumptions to produce a reasonable approximate value.

An estimate is useful when an exact value is unavailable, unnecessary or difficult to obtain. In a microscope image, for example, a cell boundary may be blurred, so its measured diameter cannot be perfectly exact. Estimation is also valuable for checking whether a calculator answer is plausible.