The picometre (international spelling as used by the International Bureau of Weights and Measures; SI symbol: pm) or picometer (American spelling) is a unit of length in the International System of Units (SI), equal to 1×10−12 m, or one trillionth (1/1000000000000) of a metre, which is the SI base unit of length.

A simplified representation of a helium atom, having an estimated (calculated) diameter of 62 picometres[1]
General information
Unit systemSI
Unit oflength
1 pm in ...... is equal to ...
   SI base units   1×10−12 m
   Natural units   6.1877×1022 P
   1.8897×10−2 a0
   imperial/US units   3.9370×10−11 in

The picometre is one thousand femtometres, one thousandth of a nanometre (1/1000 nm), one millionth of a micrometre (also known as a micron), one billionth of a millimetre, and one trillionth of a metre.[2] The symbol μμ was once used for it.[3] It is also one hundredth of an ångström, an internationally known (but non-SI) unit of length.

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