There is no set size it is more of a tradition or cultural matter.
However in the UK there exists legislation as to how much liquid should be in a pint or half pint of lager or beer. The head is not classed as part of this liquid limit and should be in addition to the liquid. Generally about a centimetre is acceptable.
An Irish lager is a beer
Lager
Corona is a lager.
in America it is lager
Mildred Lager died in 1960.
Mildred Lager was born in 1900.
Wrexham Lager was created in 1881.
Wrexham Lager ended in 2000.
Gunnar Lager died in 1960.
Gunnar Lager was born in 1888.
John Lager died in 1961.
John Lager was born in 1887.