Beer drinkers are losing out because pints often fall short of the full measure, campaigners claim.
A survey of 25 local councils found 26.6% of pints served in pubs were under-filled by at least 5%.
The Campaign for Real Ale (Camra) says the lost liquid costs drinkers around £481 million every year. It is calling on the Government bring in legislation requiring licensees to serve full pint measures.
Camra's findings were taken from 25 trading standards surveys carried out between the end of 2004 and this year. The results relate to real ale, lager, and cider.
Camra said the worst example was a pint served with 13% less liquid than it should have been.
Mike Benner, chief executive of Camra, said: "It is a disgrace that up to a quarter of all pints served in the UK are less than 95% liquid when the consumer is paying for a full pint every time."
Camra has launched an online "full pints" petition calling on the Government to end short beer measures.
British Beer and Pub Association communications director Mark Hastings said: "Pubs are packed with punters enjoying their pints, not taking out rulers to measure them.
"Our standard approach is that the head should never be more than 5%, but if you want it filled to the top, ask and we'll do it.
"All systems of weights and measures have tolerances built into them, whether it's your pint of milk, litre of petrol or bottles of pop. That's the rational and reasonable approach to this issue."
