Quadrillion may mean either of the two numbers (see long and short scales for more detail):
- 1,000,000,000,000,000 (one thousand million million; ; SI prefix peta-) – for all short scale countries; increasingly common meaning in English language usage. It is named billiard (or alternatively A Thousand Billion) in all long scale countries.
- 1,000,000,000,000,000,000,000,000 (one million million million million; ; SI prefix: yotta-) – for all long scale countries; increasingly rare meaning in English language usage.