Because 'L' is the initial (the first letter) of the word
'liter', so when you read 'L',
it's quite easy for your brain to quickly realize that the 'L'
is there in place of the
word 'liter'. At least, more quickly than if the letter were a
'D' or a 'Q'.
L is the abbreviation for liters, so 1.4 L is 1.4 liters.
2 L = 2 L
L is the abbreviation for Liters.
The metric system uses m,L, and g.
1.5 L is 1 and 1/2 liters