Size (measure of extent and scale)

Measures and units

To express size quantitatively we use units and standards that allow comparison. Length, area and volume are common measures: length for one-dimensional extent, area for two-dimensional surfaces and volume for three-dimensional space. Weight or mass is distinct from size but frequently reported alongside it. Standard units (for example, those defined by national and international bodies) make measurements consistent; see units and standards for more on how units are defined and maintained.

Scales and examples

Size spans many orders of magnitude. Typical categories include:

• Microscopic: cells, bacteria, and particles smaller than the eye can resolve.
• Human-scale: objects people manufacture and encounter daily, from clothing to furniture.
• Geological and planetary: mountains, continents and planets.
• Cosmic: stars, galaxies and larger structures of the universe.

Measuring and uncertainty

Measurement of size relies on instruments and procedures that introduce limits and uncertainty. Precision refers to how repeatable a measurement is, accuracy to how close it is to the true value. All quantitative size statements are normally given with some indication of uncertainty or tolerance, and often a simple numerical value alone is insufficient without context about how it was obtained.

Cultural and technological uses

Beyond science, size is important in design, fashion, packaging, and computing. Clothing sizes, font sizes and file sizes are conventions developed to communicate fit, legibility or capacity. In engineering, safe loads and clearances depend on accurate size specifications.

Distinctions and notable facts

Size should not be conflated with mass, quantity or importance: something large may be light, and something small may be critically important. In many fields the choice of which dimension to call "size" depends on purpose—for a sheet of paper its area matters, for a wire its length or diameter, and for a dataset its storage size.