How do you get a sense of $2.4 trillion? That's how much the Congressional Budget Office says the wars in Iraq and Afghanistan could cost over the next 10 years. It's an awful lot of money.

But not, in principle, impossible to imagine. Consider some comparisons:

Hurricane rainfall, gallons per day 2.4 trillion

Passenger miles flown in 2006 2.4 trillion

Gallons of water used in Florida every year 2.4 trillion

Estimated barrels of oil in the world before drilling began 2.4 trillion

Annual flow of Indus River, in cubic feet 2.4 trillion

(That's three times as much, by the way, as that of the Tigris and Euphrates combined.)

And there are far bigger numbers around; 2.4 trillion miles hardly gets you out of the neighborhood, galactically speaking. The stars of the Big Dipper, one of the brighter constellations, are about 458 trillion miles away.

But back to dollars. The total credit card debt in this country is about $2.4 trillion. So is the federal budget. So it's not an impossible amount to comprehend, though it may be close.

Here's a sampling of national gross domestic products:

United States $13.2 trillion

United Kingdom $2.3 trillion

Iran $222 billion

So, in effect, the U.S. is spending the equivalent of Iran's GDP over the next decade in pursuit of victory in its two neighbors.

Consider annual defense spending:

U.S. $623 billion

The rest of the world $500 billion

Iran $4 billion

But right now let's put one fairly obvious notion aside. Yes, $2.4 trillion would pay for lots of schooling or medical insurance or mortgage assistance, but it's a slightly unfair point to make. Wars are, in theory at least, one-time expenditures, rather than continuing budget items. So maybe it's one-time this year, and then one-time again the year after that, and so on, but the idea is that someday the fighting will come to an end and the U.S. won't have to spend that money anymore.

Consider, then, the cost of American wars, in 2005 dollars:

The Revolution $1.8 billion

The Civil War $67 billion

World War I $204 billion

World War II $3.1 trillion

Vietnam $532 billion

That puts Iraq-Afghanistan at the No. 2 all-time position. And it's hard to escape the realization that America's current opponents aren't spending anywhere near as much.

Or public works projects, in today's dollars:

Hoover Dam $2.4 billion

Interstate highways $129 billion

The moon program $135 billion

Proposed California bullet train $40 billion

Proposed Freedom Tower on World Trade Center site $12 billion

The Marshall Plan $9.3 billion

All those together equal less than one-seventh of the current war-cost estimate. You could build 1,000 Hoover dams for the same money.

How much is $2.4 trillion? Look at real estate assessments:

New York City $671 billion

Maryland $547 billion

Texas $1.2 trillion

Add them together, and sell them, and you could pay for the war.

Or consider federal expenditures. Up to World War II, they totaled almost exactly $2.4 trillion, in today's dollars. That is, all the money spent by the federal government between 1789 and 1941 comes to the same as the bill for the wars in Iraq and Afghanistan.

If you believe the war in Iraq is largely about oil, it's worth noting that the U.S. consumes about 7.3 billion barrels a year. If that level were kept constant over the next decade, you could say that U.S. war spending amounts to about $33 a barrel. Is that a good bargain, or what?

- Will Englund