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.