I don't like to guess. I have an SP (Swissmex) backpack sprayer with diaphragm pump. How much does it cover per gallon? I sprayed water into a 4 ounce measuring cup, and timed it with a stopwatch, (takes about 13 seconds). Repeated 4 times. That equals about .31 ounces per second. I then sprayed a concrete drive and measured how much one quart would cover, three times. I converted to square feet per gallon. I measured coverage at 773 square feet per gallon--from my backpack sprayer. Naturally a lot depends on the pressure and how much you are pumping. And of course the nozzle type on your set up can be different. And there is a chance that the output may vary depending on where you set an adjustable nozzle. And the height where you hold the nozzle could affect the spray coverage. And walking speed and width of swath can vary. How much does your backpack cover per gallon? With what nozzle. How many seconds for 4 ounces? I just hate it when the new guys just say "Oh, the salesman told me my backpack covers exactly 1000 square feet per gallon."