We must not forget the measuring system so beloved of UK newspapers:
Length: London omnibuses, as in "As long as three London buses"
Area (large): Wales, as in "Three times the size of Wales"
Area (small): Football (soccer) pitches, as in "An area twice the size of a football pitch". An elastic unit, as football pitches can vary in area, within certain limits
Volume (large): The Albert Hall, as in "enough to fill the Albert Hall three times over"
Volume (small): Olympic swimming pools "as big as five Olympic pools"
Small diameter: a human hair, though this is used only in the singular and as a maximum, as in "half the thickness of a human hair".
Andy