Estimate

Definition

A calculation that gives a sensible approximate value rather than an exact measurement.

Used by Edexcel and OCR

Paper 1, Paper 2

A value judged to be reasonably close to the true value, usually found using rounded quantities or assumptions.
Atoms differ in size, there may be spaces within a structure, and the estimate may use a radius, diameter or bond length depending on the context. The calculation is valuable because it shows why even a tiny object visible to us contains an enormous number of atoms.
Revise: Mathematical Applications
A reasoned approximate value found from suitable known information rather than an exact measurement.
Revise: Mathematical Applications

1
An estimate should show a sensible assumption and appropriate rounding; do not imply greater precision than the data justify.
2
When asked to estimate, give a sensible approximate value with a unit; excessive precision is not appropriate.
3
Show powers-of-ten working in an estimate and state any simplifying assumption, such as arranging atoms edge to edge.

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Specification CM2.1ii, CM2.2i, CM2.3iii · Paper 1 (Foundation), Paper 3 (Higher)

A value close to the exact result, often produced by rounding numbers before calculating.
Rounding for an estimate is different from rounding a final calculated result. To estimate, values are often rounded first—commonly to one significant figure—so that the arithmetic becomes simple and the approximate size of the answer can be checked. In an ordinary calculation, however, use the original values and round only at the end.
Revise: Significant Figures
A calculation giving a sensible approximate value rather than an unnecessarily precise answer.
Revise: Scale Estimation
An approximate value that is sufficiently close to show the correct size or scale.
Revise: Scale Estimation

Paper 1 (Foundation), Paper 2 (Foundation), Paper 3 (Higher), Paper 4 (Higher)

Powers of ten make estimates manageable.
Revise: Size and scale of atoms
A judgement of an approximate value based on suitable reference values and comparisons.
Revise: Scale and definition of nanotechnology