Countless lives are being put at risk by motorists who get behind the wheel in the mistaken belief that they are under the drink-drive limit, according to a survey.
The huge variety of drinks is said to have added to the confusion
Eight out of 10 drivers are confused about the alcohol content of drinks and do not understand "how much is too much", motoring organisation the RAC said.
Among the seven million people happy to drive after drinking beer, wine or spirits, the majority consume double the number of alcohol units they think they have, the survey of 800 people claimed.
The RAC said the problem had been made worse by the introduction of new drinks and called on the government and manufacturers to improve awareness of just how strong they are.
The current alcohol content system, which was introduced 15 years ago, needs bringing up to date, the RAC said.
Standard (175ml) glass of wine - 2 units
Large (250ml) glass of wine - 3 units
Pint of standard lager - 2.3 units
Pint of premium lager - 2.8 units
Pint of strong cider - 4.7 units
It said the market has been flooded with more types of drink than ever before, with the fashion for premium strength lagers just part of the problem.
Many pubs now serve double measures of spirits as standard and wine can no longer be bought in measures equivalent to one unit of alcohol following the decline of 8% strength brands.
One standard glass of wine these days is actually equivalent to two units, the RAC explained.
The legal drink-drive limit is 80mg per 100 millilitres of blood, but this cannot easily be translated into alcohol units as it can be affected by build, sex, whether food has been eaten, and a host of other factors.
34% of men drink and drive, compared with 23% of women
Those aged 35-54 are least likely to drink and drive
Those in the higher social grades (ABC1) are slightly more likely to drink before driving
RAC spokeswoman Nicola Thunhurst told BBC Radio 4's Today programme: "People really don't have an awareness of the number of alcoholic units that are in the drinks they are consuming and they're actually basing their knowledge on quite out of date information."
She said the idea that you could work out how much you can safely drink without going over the limit was simply not true.
"It's really best to never drink any alcohol before driving because you simply can't tell how much you've had to drink and what sort of effect it will have on you," she added.
The RAC says millions of motorists regularly - and unwittingly - drink more than they realise before getting into their cars.
It said the government must "increase public awareness of alcohol units and work with the drinks trade to improve the labelling on alcohol".