For those who struggle to balance their checkbooks every month, it might be difficult to comprehend the meaning of Thursday's vote by the Senate to raise the government debt limit to nearly $9 trillion.

After all, how much is a trillion?

It's the number one followed by 12 zeros. But that doesn't shed much light on just how deeply in debt the federal government is that it must pass a law enabling it to borrow up to $8.965 trillion.

"It's hard to understand what a trillion is. I don't know what it is," confessed Senate Budget Committee Chairman Judd Gregg, a New Hampshire Republican, this week when debating the government's staggering fiscal obligations.

It doesn't help that the standard hand-held calculator comes nowhere close to computing numbers in the trillions. About the best it can do is 99,999,999.

John Nolan, a mathematics professor at American University in Washington, said that a trillion is "not a big number at all" for some theoretical problems. "But in terms of practical numbers it's just overwhelming."

So he conjured up a spending spree, something Americans might be able to relate to. "If you spent a million dollars a day for a million days (2,739 years)," you'd hit $1 trillion, Nolan observed.

To spend $1 trillion in the average American life span of 77 years, you'd have to be on a lifetime spending spree of about $35,580,857 and change every day from birth.

Don Albers, associate executive director of the Mathematical Association of America, said to forget about all the fancy numbers. "I don't think the problem so much is understanding that number as just understanding whether they've got more money coming in than is going out," he said.

And that's the rub. The federal government has been on a spending binge. Just since 2002, the Republican-controlled Congress has had to hike the Treasury Department's credit card limit four times, for a total of more than $3 trillion.

Congress can take some comfort in knowing that at this rate, it will take a very long time to exhaust the trillions and spill into the quadrillions. "Let's hope that they won't be using that" number ever, Albers said.