For gravity-driven flow, the water pressure depends on the height of the water surface in the tank above the outlet at the sprinkler. The size and shape of the tank will affect how quickly the water surface drops as the tank empties, but the volume of the tank does not directly affect the pressure. Here is a page that describes the basic equations and has a calculator to convert between pounds/ square inches and inches of water.
I don't know how much pressure your particular sprinklers require to operate, but lets assume they can 20 psi. Twenty psi is equivalent to 554 inches, or 46 feet of water.
So, unless you live in a 5 story building, you will probably need to use a booster pump, or a different type of irrigation, such as drip irrigation.