So I was reading the science news over at the BBC when I came across this article:

Although there are still those who argue over the US and “former UK” definitions of figures such as a billion and trillion, according to Michael there is now basic agreement that a trillion is a thousand billion and a billion is a thousand million.

Maybe it’s my American-centric upbringing, but was there really a debate about this? I went and consulted a few dictionaries. Merriam-Webster says:

1 — see NUMBER table
2 : an indeterminately large number

The “number table” gives the following (American, British, integer) triples: (billion, milliard, 10⁹), (trillion, billion, 10¹²), and (quintillion, trillion, 10¹⁸). Apparently 10ⁿ where n = 3 (mod 6) and n > 14 don’t warrant their own name — they can be a “thousand 10^{n – 3}.”

The regional bias is clearer in the American Heritage versus OED. The American Heritage Dictionary puts 10¹² first:

1. The cardinal number equal to 10¹².
2. Chiefly British The cardinal number equal to 10¹⁸.

The OED has its own bias:

The third power of a million; a million billions, i.e. millions of millions. Also, orig. in France and local U.S., a thousand ‘billions’, or 10¹² (i.e. the traditional English billion: see BILLION): this sense is now standard in the U.S. and is increasingly common in British usage.