Billion (number)

Definition and notation

Two counting systems give different values for billion:

• Short scale — billion = 1,000,000,000 = 10^9. This is the usage in contemporary American and common British English and in most international scientific contexts.
• Long scale — billion = 1,000,000,000,000 = 10^12. This sense was once common in the United Kingdom and remains in use in some languages and older documents.

To avoid confusion, scientific notation (for example 1×10^9) or SI prefixes such as giga- (1 gigabyte = 10^9 bytes in SI) are often used. In everyday speech some people also say "thousand million" or use local terms like "milliard" for 10^9 in certain languages.

History and etymology

The English word derives from French, where -illion forms were modelled on million; the prefix bi- originally suggested a second power (a square) of a million, which led to the long-scale meaning of 10^12. Over the 19th and 20th centuries many English-speaking countries shifted to the short-scale convention; for example the United Kingdom officially adopted the short scale in the 20th century.

Uses and examples

Billion is widely used in finance, demography, astronomy and computing. Typical examples include national budgets and corporate valuations denominated in billions of currency units, and world population figures expressed in billions of people. Conversions and perspective help: one billion seconds is roughly 31.7 years, and one billion meters is about 1,000 kilometers.

Ambiguity and best practice

Because the word can mean different powers of ten in different contexts, writers and speakers should be explicit when precision matters. Use numerical forms, scientific notation, SI prefixes (giga-), or clarify the scale ("10^9" or "thousand million") when communicating across languages or in technical material.