Use figures with million, billion, or trillion in all except casual uses. For example,
- I’d like to make a billion dollars.
- The nation has 1 million citizens.
- I need $8 billion.
- The government ran a deficit of more than $1 trillion.
Do not go beyond two decimal places. For example,
- 7.51 million people
- $256 billion
- 7,549,899 people
Decimals are preferred where practical. For example,
- 1.5 million
- 1 1/2 million
Do not mix millions and billion in the same figure. For example,
- 2.5 billion
- 2 billion 500 million
Do not drop the word million or billion into the first figure of a range. For example,
- He is worth $4 million to $5 million.
- He is worth $4 to $5 million.
Unless that is, of course, you actually mean $4.
Note that a hyphen is not used to join the figures and the word “million” or “billion,” even in this type of phrase,
- The president submitted a $300 billion budget.
In headlines, abbreviate only millions, billions. For example,
- $5M lawsuit, $17.4B deficit
See also AP Style Numbers.