To know for sure, you must consult your owner's manual or a reliable online resource like a repair manual specific to your truck (providing the axle ratio is known). Looking at the differential itself for a sticker with the capacity is also helpful.
Typically, it will hold between 1 and 1.5 quarts, but this is just a general range. Never rely on this number; consult your manual. Using the wrong amount can damage your differential.
