Atoms are extremely small. A typical atom is about 1 × 10-10 m across. This is the same as 0.1 nanometres, where the abbreviation is nm. One nanometre is one billionth of a metre, which is 1 × 10-9 m.
A small molecule is made of a few atoms joined together, so it is a little bigger than a single atom. Small molecules are typically between about 0.1 nm and 1 nm across.
The order of magnitude of a quantity is its size to the nearest power of ten. A human hair is about 1 × 10-4 m wide. This is about a million times wider than an atom, so the hair is six orders of magnitude bigger. Atoms and small molecules are far smaller than anything you can see with the naked eye.