A picometre (alternative picometer) (symbol pm)'s a unit of length in the metric system, equal to one trillionth (short scale) or one billionth (long scale), for example (1/1,000,000,000,000) of a meter, which's the current SI base unit of length. It can be written in scientific notation as 1×10−12 m (scientific notation) or (engineering notation ) — both meaning . It equals a millionth of a micrometer (formerly called a micron), and was formerly called micromicron, stigma, or… (More on Picometre)