The volume selected for calculations in gas laws is typically the amount that a mole of gas occupies, which is equivalent to its molecular weight in grams and measures 22.4 liters at standard temperature and pressure. This quantity helped establish what is now known as Avogadro's number. Accurately measuring this number has been challenging, but it is currently estimated to be about 6.02214 × 10²³.

This immense figure can be conceptualized better by imagining a vast number of unpopped popcorn kernels. If one were to spread this number of kernels across the entire United States, they would form a layer that reaches nine miles deep. This vivid illustration highlights the sheer scale of Avogadro's number, reflecting the extensive quantity of molecules present even in small amounts of gas.