Rounded Large Numbers
19.3.1 Rounded Large Numbers
Rounded large numbers, such as those starting with million, should be expressed with numerals and words.
The disease affects 5 million to 6 million people. [Note that the word million is repeated to avoid ambiguity.]
The word million signifies the quantity 106, while billion signifies the quantity 109. Although billion has traditionally signified 1012 (1 million million) in Britain, many British medical journals1 now use billion to indicate the quantity 109. A number may be expressed in million rather than billion if the latter term could create ambiguity. In that case, the decimal should be moved 3 places to the right. Trillion should be used to denote the quantity 1012.
The projected budget is £2.5 billion.
Or: The projected budget is £2500 million.
The budget deficit is expected to expand to $1 trillion by 2020.