A picometre is a measurement. It is one millionth of a billionth of a metre. It is also one trillionth of a millimetre. This is very small. Many atoms are larger than this. A picometer is 1×10−12 m (1 / 1,000,000,000,000 m). 1 picometer equals 0.001 nanometre or 1000 femtometres.