Donated blood has a shelf life just 42 days but most Australians believe it lasts forever, according to a new national survey.

Seriously ill patients could be missing out on life-saving blood transfusions because Australians don't realise donated blood has a very short shelf life.

Donated blood doesn't even last two months, yet new research reveals there is a misconception in the community that it lasts forever.

A survey by the Australian Red Cross Blood Service found 90 per cent of people did not know how long donated blood could be kept.

If they had known it only lasts 42 days, more than a third of participants said they would have been more likely to donate.

"Blood is a precious and finite resource, and blood donations don't last forever. In fact, the red cell component of a donation only lasts 42 days," said Blood Service spokesperson Jennifer Campbell Case.

The survey also uncovered similar misconceptions about blood donor rates, with Australians overestimating how many people donate blood and underestimating how much blood is needed.

More than half of the respondents thought at least one in 10 people were blood donors.

"But the real figure is much less; only one in 30," Ms Case said.

"And 80 per cent either didn't know or underestimated the number of blood donations Australian patients need each year," she said.

The findings have prompted the Blood Service to launch a new campaign to recruit 8000 new blood donors every month.

"We're hoping that our new campaign, which educates donors on the 42-day shelf life of blood, will motivate more people to donate today and donate regularly," said Ms Case.