WASHINGTON—Just how rich is Mitt Romney? Add up the wealth of the last eight presidents, from Richard Nixon to Barack Obama. Then double that number. Now you're in Romney territory.

He would be among the richest presidents in American history if elected -- probably in the top four.

He couldn't top George Washington who, with nearly 60,000 acres and more than 300 slaves, is considered the big daddy of presidential wealth. After that, it gets complicated, depending how you rate Thomas Jefferson's plantation, Herbert Hoover's millions from mining or John F. Kennedy's share of the vast family fortune, as well as the finer points of factors like inflation adjustment.

But it's safe to say the Roosevelts had nothing on Romney, and the Bushes are nowhere close.

The former Massachusetts governor has disclosed only the broad outlines of his wealth, putting it somewhere from $190 million to $250 million. That easily could make him 50 times richer than Obama, who falls in the still-impressive-to-most-of-us range of $2.2 million to $7.5 million.

"I think it's almost hard to conceptualize what $250 million means," said Shamus Khan, a Columbia University sociologist who studies the wealthy. "People say Romney made $50,000 a day while not working last year. What do you do with all that money? I can't even imagine spending it. Well, maybe ..."

Of course, an unbelievable boatload of bucks is just one way to think of Romney's net worth, and the 44 U.S. presidents make up a pretty small pond for him to swim in. Put alongside America's 400 or so billionaires, Romney wouldn't make a ripple.

So here's a look where Romney's riches rank -- among the most flush Americans, the White House contenders, and the rest of us:

--Within the 1 percent:

"Romney is small potatoes compared with the ultra-wealthy," said Jeffrey Winters, a political scientist at Northwestern University who studies the nation's elites.

After all, even in the rarefied world of the top 1 percent, there's a big difference between life at the top and at the bottom.

A household needs to bring in roughly $400,000 per year to make the cut. Romney and his wife, Ann, have been making 50 times that -- more than $20 million a year. In 2009, only 8,274 federal tax filers had income above $10 million. Romney is solidly within that elite 0.006 percent of all U.S. taxpayers.