How much saving does a happy retirement require? That's one of the fundamental questions underlying all the "golden year" planning for millions of Americans, and a magazine's survey suggests the answer is elusive for many of us.

About a third, 37 percent, said they think they'll need only $500,000 saved, while about a quarter, 24 percent, said $1 million. About the same number, 23 percent, said they don't know.

But they are, apparently, confident they will be OK when they stop working. Sixty-three percent said they feel "on track" for their retirement finances and 62 percent said they're pretty certain they won't need to work then.

The survey for Kiplinger's Personal Finance magazine involved telephone surveys of 1,017 people.

"Most Americans feel like they are headed in the right direction, but they aren't certain where the finish line lies," said Fred W. Frailey, the magazine's editor.

"Successful retirement preparation requires a well-defined goal and a disciplined plan for reaching it. We estimate that a retiree would need to have $1 million saved to achieve $50,000 of annual income, at a 5 percent withdrawal rate."