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What is a billion?

What constitutes a billion is a source of occasional confusion.  In official UK statistics the term is now used to denote 1 thousand million – 1,000,000,000.  Historically, however, in the UK the term billion meant 1 million million – 1,000,000,000,000 – but in the United States the term was used to refer to 1 thousand million. The US value had, however, become increasingly used in Britain and the Prime Minister, Harold Wilson confirmed in a written reply in 1974 that the meaning of “billion” would be thousand-million, in conformity with international usage.

The Oxford English Dictionary explains why UK and US usage differed.

billion, purposely formed in 16th c. to denote the second power of a million (by substituting BI- prefix for the initial letters), trillion and quadrillion being similarly formed to denote its 3rd and 4th powers. The name appears not to have been adopted in Eng. before the end of the 17th … Subsequently the application of the word was changed by French arithmeticians, figures being divided in numeration into groups of threes, instead of sixes, so that F. billion, trillion, denoted not the second and third powers of a million, but a thousand millions and a thousand thousand millions. In the 19th century, the S. adopted the French convention, but Britain retained the original and etymological use (to which France reverted in 1948).

Since 1951 the U.S. value, a thousand millions, has been increasingly used in Britain, especially in technical writing and, more recently, in journalism; but the older sense ‘a million millions’ is still common.

Oxford English Dictionary, 1989 ed

The text of the 1974 Harold Wilson PQ:

“Billion” (Definition)

Mr Maxwell-Hyslop asked the Prime Minister whether he will make it the practice of his administration that when Ministers employ the word “billion” in any official speeches, documents, or answers to Parliamentary Questions, they will, to avoid confusion, only do so in its British meaning of 1 million million and not in the sense used in the United States of America, which uses the term “billion” to mean 1,000 million.

The Prime Minister: No. The word “billion” is now used internationally to mean 1,000 million and it would be confusing if British Ministers were to use it in any other sense. I accept that it could still be interpreted in this country as 1 million million and I shall ask my colleagues to ensure that, if they do use it, there should be no ambiguity as to its meaning. (HC Deb 20.12.1974 c711-2W).

This definition of a billion is now known as the short scale – where each new term for a number above a million is one thousand times greater than the previous one. The historical definition of a billion is now known as the long scale – where each new term for a number above a million is one million time greater than the previous one.

Other units

The table below gives a selection of other small and large numbers, their (short scale) name, SI prefixes and associatied scientific notations. The format of scientific notations is 10n where n is the total number of zeros. Hence 109 is 1,000,000,000 or one billion. Where n is negative the number is less than one and n refers to the number of decimal places.

Units table

SI: The Système International d’Unités or International System of Units. SI prefixes are applied to SI base units such as metre, second or watt.

Hence if we are looking at energy where the basic unit is a watt hour (Wh) then a trillion watt hours is known as a terawatt hour (TWh) which is equivalent to 1012 or 1,000,000,000,000 watt hours. A billionth of a metre is known as a nanometre (nm) which is equivalent to 10-9 or 0.000000001 metres.

Increases or decreases in scale can quickly become hard to fully comprehend, as can their cumulative impact. The 1977 short film Powers of Ten illustrates the impact of changes in scale from extremely large to extremely small dimensions.

Other statistical literacy guides in this series:

 How to understand and calculate percentages

 Index numbers 

 Rounding and significant places

 Measures of average and spread

 How to read charts

 How to spot spin and inappropriate use of statistics

 A basic outline of samples and sampling

 Confidence intervals and statistical significance

 A basic outline of regression analysis

 Uncertainty and risk

 How to adjust for inflation


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