Why a British Billion Used to Be a Thousand Times Bigger

On 20 December 1974, a Conservative MP called Robin Maxwell-Hyslop asked the Prime Minister to do something quite specific: he wanted Harold Wilson to commit that British government ministers would only ever use the word "billion" in its traditional British sense, of one million million, and not in the American sense, of one thousand million. Wilson, in a one-paragraph written reply, said no. From that point on, in any official document or ministerial answer, a British billion would mean what an American billion meant. Nine zeros, not twelve. A thousand times smaller than the word had meant the day before.

Anyone in the UK who learned arithmetic before about 1975 was taught a billion that the government no longer uses.

The question Wilson said no to

The exchange is in Hansard for that date, under the heading "Billion (Definition)". Maxwell-Hyslop's question is detailed and slightly defensive: he wants ministers to keep using the British billion to avoid confusion with the American one. Wilson's reply gives the opposite reason. The word is now used internationally to mean a thousand million, he says, and it would be confusing for British ministers to use it in any other sense. He concedes that in the country at large the older meaning is still around, and asks his colleagues to make sure there is no ambiguity when they use the word.

This was less a sudden conversion than the moment the government caught up with everyone else. Banks, the financial press, and most British newspapers had already been using the American billion for years. Winston Churchill had remarked decades earlier that for all practical financial purposes a billion was already a thousand million. The 1974 written answer is the moment the government stopped pretending otherwise.

Two scales, one word

There are two systems for naming very large numbers, and they disagree about every word after a million.

The long scale, used historically in Britain and still used in much of continental Europe, scales each new word up by a factor of a million. A billion is a million million. A trillion is a million billion. The names rise in jumps of six zeros at a time.

The short scale, used in the United States and now officially in the UK, scales each new word up by a factor of only a thousand. A billion is a thousand million. A trillion is a thousand billion. The names rise in jumps of three zeros at a time.

The same word, billion, does different work in each system. A traditional French billion is still a million million. A modern American or British billion is a thousand million. The two billions are not close. One is a thousand times the other. This is why careful business reports sometimes spell it out, writing "one thousand million" or "10⁹" rather than relying on the word itself.

Why this is not the same problem as not feeling the size

How Long Does It Take to Count to a Billion? is about a different problem. That piece is about the human brain compressing very large numbers, so that a million and a billion both register as "very big" even though one is a thousand times the other. That gap is cognitive, and it does not go away when you know it is there.

The British and American billion gap is not cognitive. It is linguistic and historical. Two definitions of the same word, both of them correct, used by different people in different places at different times. A grandparent who learned the older British meaning and a grandchild who learned the American one can use the same word at the same dinner table and mean numbers that are a thousand times apart.

Both effects are at work whenever the word turns up in a conversation about big numbers. Noticing which billion is being used is the easy fix. The cognitive compression is the slower one.

What this doesn't mean

The short-scale billion was not chosen because it was better. It was chosen because it had already won. The Wilson written answer reads less like a decision and more like an acknowledgement. The British government was the last formal holdout, and by December 1974 even the holdout had stopped holding out.

It is also worth saying that older British books are not wrong. A 1960s science textbook that uses billion to mean a million million is using the word correctly for its time. It is using a definition that has since been quietly replaced. The book has not aged. The word has.

The conversation worth having

Ask a child how big a billion is. Then ask a grandparent the same question. The interesting moment is not in either answer, but in the gap between them, especially if the grandparent grew up in Britain before the 1970s. The same word, said in the same language, has carried two different numbers within the lifetime of people who are still alive.

A child who can hold both versions of a billion in their head, even briefly, has learned something more useful than the size of either one. They have learned that the words on the page do not always agree with the words their grandparents grew up with, and that a number can quietly mean something different depending on when and where it was written.

The number on the page does not always agree with the number in your head. Sometimes the brain is compressing. Sometimes the dictionary has moved under your feet.