That is the finding of a pensions survey by Prudential.
Nearly two in five (39 per cent) either said they had no idea what the state pension is worth or think it is worth more than the £113.10 a week payable from April 2014.
Around one in six (17 per cent) overestimated the value of the state pension by at least £880 a year, according to the study.
The Prudential research also highlighted the importance of the state pension to people planning to retire this year.
On average it makes up 35 per cent of an individual's total expected retirement income, which is the same proportion on average that is expected to come from company pension schemes.
Despite the widespread reliance on the state pension, there is confusion among those planning to retire this year about how much it is worth for an individual.
Vince Smith-Hughes, retirement income expert at Prudential, said: "It is important to avoid falling into the trap of overestimating the contribution that the state will make to your retirement income, as the state pension alone is barely sufficient."
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Women are more reliant on the state pension than men – on average it makes up 42 per cent of women's expected retirement incomes compared with 28 per cent for men.
Mr Hughes said: "The introduction of auto-enrolment into workplace pension schemes is helping to encourage saving, and along with plans for a flat rate state pension from 2016, small steps are being taken to improve retirees' prospects."
"However, simply saving as much as possible as early as possible in your working life and seeking professional financial advice in the run up to retirement will help to make the most of your savings when you're ready to stop working."