James Hamilton of Econbrowser puts a trillion dollars into perspective this way:
A trillion dollars is about the total amount collected in [individual] income taxes by the U.S. federal government in fiscal year 2006– $1.04 trillion, if you're curious to use the exact number. That gives me a simple rule of thumb for personalizing these numbers. If I want to know what an additional trillion dollars in government borrowing or spending will mean for me, I just imagine what it would be like to pay twice as much in federal income taxes for one year.
So, for example, with the President's proposed budget calling for deficits of $1.75 trillion for 2009 and an additional $1.17 trillion for 2010, after 3 years of paying twice as much as I paid in 2006, I'd have about paid off my share of the bill for the first two years of the proposal.
But a commenter on his site has another way of looking at it:
I think this is really misleading since it assumes you would double all equal tax rates equally and pay for the whole thing in 1 year — which is downright silly.
The top tax bracket is 35% – it was 92% in 1952.
A tiny change in the top tax bracket (like 3%… I mean we are talking about adjusted gross income over $357K) would generate $1 trillion in revenue in only a few years. I mean you should know this since that's how we got rid of our > $1 trillion surplus. Or alter corporte income tax accounting rules to raise a miniscule amount from corporations.