How much hydraulic fluid is in a jet airliner?
FCOM for the A320 describes 3 independent hydraulic systems, with accumulation reservoirs for each at 6.5L,12.5L &amp; 14.5L (1.7USG,3.3USG&amp; 3.8USG) respectively, so +33.5 liters is a good bet, which translate to 26-33 kgs depending on fluid type. 

Note that more fluid will be available in the system, but how much exactly you will need a mechanic to answer.