A decimal submultiplier prefix in SI, signifying 10⁻¹², or one trillionth, of the unit to which it is prefixed. The origin of this prefix is uncertain; it may have been suggested by the Italian “piccolo,” meaning small. Symbol, p.

The pico-’s progress toward official acceptance began in 1940 with a draft proposal made by technical committee ISA-9 d 2 of the International Federation of National Standardizing Associations, the predecessor of the ISO. Its legalization was delayed by World War II, but in 1948 the General Assembly of the International Union for Pure and Applied Physics approved it, as recommended by its Commission on Symbols, Units and Nomenclature. The prefix was widely used, but not actually approved until the adoption of SI by the 11th CGPM in 1960.

In Chinese, the pico- is weiwei.

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