If you said "one trillion" you're counting like I do, and other Americans, scientists, and UK folks that learned after 1974. If, however, you said "one billion" you either missed a set of zeros or are using the traditional British counting method or the European counting method, still frequently used (according to a number of different websites).

How about 1,000,000,000?

If you said "one billion" that's the American and scientific counting system. If you said "one thousand million" you probably learned in Britain before 1974. Finally, if you said "one millard" (or maybe "one milliard", my sources are inconsistent) you're using the European system.

A billion isn't a billion the world around.

Why is this important? Because you might be off by many orders of magnitude when thinking about such things as national debts. If you hear that the US is giving out nearly a trillion dollars, you might think that's 10^18th (uhm, this: 1,000,000,000,000,000,000). In our system, though, that's a quintillion. A trillion is a million times less! That is, it's 10^12th (1,000,000,000,000). That's a huge difference!

What gives?

Simply put, one counting system bases the number prefix on one less than the power base 1000. That is, the American system is based on 1000^n where n minus 1 determines the prefix to use. So, for instance, 1000^4 is a trillion. Note the "tri" part of trillion and 100^7 is a septillion, and so on.

The other system, though, can be thought of as based on the power base 1000000. That is, 1000000^3 is one trillion in this system and 1000000^7 is a septillion. For those number with that land in between the powers, you put a thousand in front of it or it's an "ard" instead of an "ion" (the actual suffix is llion or tillion, depending on other rules from latin).

Also interesting, but slightly unrelated, is that the latin prefixes are exhausted for powers greater than 1000000 (e.g. 1000^1000001 and higher ("one thousand to the power of million one")). At that point, the last prefix -- millia -- starts repeating. Also, at the point, human brains explode trying to imagine what these numbers might mean. Seriously. According to Wikipedia, there may only be 10^80 atoms in the observable universe. Really, that's a small number -- only one hundred quinvigintillion.

Here's one for ya: If we can talk about numbers larger than the number of observable atoms (MUCH larger), what do they represent in the real world?

Sources: Wikipedia, chongo on numbers, Jim Loy, Quadrillion Corp (where I first saw reference to a different system)