Atoms are incredibly small. The typical size of an atom is 1 × 10-10 m, which is 0.1 nanometres (nm). A nanometre is one billionth of a metre, so 1 nm = 1 × 10-9 m. An atom, at 0.1 nm, is smaller than one nanometre.
Small molecules are made of just a few atoms, so they have about the same size. Atoms and small molecules are both typically 1 × 10-10 m across.
A number such as 1 × 10-10 is written in standard form. Giving a size to the nearest power of ten is called its order of magnitude. Atoms and small molecules therefore have the same order of magnitude.
To get a feel for the scale, a human hair is about 1 × 10-4 m wide. Each step of 10 in the power of ten makes a number ten times bigger: 103 is one thousand and 106 is one million.