It's not exactly news that Americans aren't all that savvy on how much money they'll need to retire.

But a new survey points out that they're really behind the curve when estimating how much of their income they should be saving to finance those days rocking on the porch — assuming that they actually can save that much.

The survey, conducted by Morning Consult and released by the Financial Services Roundtable, found that approximately a third of respondents either think that saving less than 10% of their pay toward retirement will cover their needs or aren't sure how much they should be saving.

Considering that about two thirds think they can get through retirement on less than $1 million, or aren't sure how much they'll need, that might be expected.

What's scary is that 8% believe that they can live out their lives on a nest egg of just $150,000 to $250,000.

Another 14% think half a million or less will do the trick.

Just a third think that they'll need $1 million or more to see them through.

A surprising 19% think that saving 5% of their pay will be enough to pay all their expenses in retirement, while the majority were a bit more sensible:

• Thirty-three percent voted for 10%

• Twenty percent were more realistic at 15%

• Fifteen percent were most realistic (or most pessimistic) and said saving more than 15% of their pay would be necessary

Thirty-five percent, however, were savvy enough to say they want a defined benefit plan from their employer rather than a 401(k), and 45% want their employers to kick in matching contributions to their 401(k)s.

And overall, respondents seem to appreciate how vital it is to have employer-sponsored retirement benefits.

Ninety-four percent said it was very important (77%) or somewhat important (17%) to have retirement benefits from an employer.