Why is a billion different in US to UK?

Answer 1

The US and UK use two different systems:

• The US uses a short notation system. That means that a billion is one thousand times one million, a trillion is a thousand times a billion, and so on. The prefix to -illion determines how many extra groups of three zeroes are appended to the number for a thousand (1 000).
• The UK uses what is referred to the long system. The prefix looks at how many groups of six zeroes there are in the number, i.e. one million has one group of six, billion has two groups of six, and so on. The long system also has names for number between each -illion, each of which is suffixed with -illiard. So one thousand million is one milliard, one thousand billion is one billiard, and so on. (Just as a note, milliard can also be referred to a sesquillion.)

So, one billion in the US is the same as one milliard (or sesquillion) in the UK.

P.S. The UK has recently begun adopting short notation, so now only the French and Germans have the long system in regular usage (with various proponents of it, such as myself, scattered in various other countries).

Answer 2

It depends on what you mean. A billion is the same everywhere 1-3 digit numbers with 9 zeros, e.g. 350 000 000 000. If you are talking about currencies, as of 4th May 2011, one Australian dollar is equivalent to 1.09 US dollars, thus A$1 000 000 000 will be equal to US$1 090 000 000. Therefore, the Aussie dollar is more valuable than the US dollar. Thanks.