A picometre (American spelling: picometer, symbol pm) is a unit of length in the metric system, equal to one trillionth (1/1,000,000,000,000) of a metre, which is the current SI base unit of length. It can be written in scientific notation as 1×10−12 m (engineering notation) or (exponential notation) — both meaning . It equals a millionth of a micrometre (formerly called a micron), and was formerly called micromicron or bicron (and written as µµ). It equals a hun… (More on Picometre)