The best thing to do with YOUR equipment is a "dry" run with just water. Find a known size of ground, 1 acre works best...pick rate of travel you are comfortable with apply water to that 1 acre. When finished, figure out how much water is missing from your tank and you now have a "calibrated" rate for your sprayer/vehicle.
My 25 gallon boomless fimco on my ATV could get about 2 acres at 6-7 mph, it sprayed a wide swath.
My 55 gallon JD UTV sprayer with a boom gets about 2.5 acres on a full tank at 6-7 mph.
High level of variance there, it pays to know your equipment.
ETA, this is assuming you aren't messing with the pressure regulator or relief valve. Keep as many things constant as you can; speed, pressure, etc.