ball-park figure informal
ball-park estimate informal
ball-park amount informal

Well, I'm wondering if you could give me a ballpark estimate of how long I'm going to be locked up.

Frank Vardy, a demographer in the Department of City Planning, said he considered 60,000 "a good ballpark estimate."

Va: I gave him a ballpark estimate, yes.

He says, however that this calculation has "a lot of noise in it" and is a "ballpark estimate."

Can you make a ballpark estimate?

Mr. Gorbechev backpedaled quickly, saying that number was just a ballpark estimate.

As it happens, $20 billion is not a bad ballpark estimate for the added cost of Mr. Bush's planned surge in troops.

The university says its estimates are accurate for those with low or high incomes, and "a good ballpark estimate" for those in the middle.

A student goes to the website and offerings from different loan providers are given, and SimpleTuition offers what one source described as a ballpark estimate.

When you're counting calories, it's an easy way to get a ballpark estimate.