Picometre

The picometre, symbol pm, is a unit of length in the International System of Units (SI). It equals 10^-12 metres. The prefix pico- denotes one trillionth of a unit. The term can be spelled picometre (British English) or picometer (American English); the plural forms are picometres or picometers.

In relation to other length units, 1 picometre is 0.001 nanometres, since 1 nm = 10^-9 m. Conversely, 1 metre equals 10^12 picometres. This yields common conversions such as 1 cm = 10^10 pm and 1 nm = 1000 pm. Picometre-scale distances are routinely encountered in atomic and molecular scales, as well as in some high-precision measurements.

Typical uses and contexts include describing atomic bond lengths and interatomic spacings in crystals (often on the order of a few hundred picometres), lattice constants, and the thickness of ultra-thin films (for example, graphene sheets have thicknesses around 340 pm). The unit is also relevant in areas such as X-ray crystallography, nanotechnology, and certain spectroscopic and metrology applications that probe features at sub-nanometre scales.

Measurement and standards: picometre measurements require advanced instrumentation and calibration, including electron or scanning probe microscopy, X-ray diffraction, and other high-precision metrology techniques. As a standard SI unit, pm is widely recognized in scientific literature for describing extremely small lengths.

See also: nanometre, angstrom, femtometre.