I have a 15 gallon sprayer that attaches to the 4 wheeler very easily. 15 gallons is exactly enough to do one acre of land if you do 4 MPH. 15 gallons per acre is also the reccomended amount for herbicides. Sometimes I wish I had bought the larger sprayer but the 15 does well for me. The biggest plot we have is just under 2 acres so we deal with refilling and remixing. I found the best price for my sprayer at Tractor Supply. I guess if you have bigger plots it may be a good idea to go with a bigger sprayer but for what we have ours works just fine. TGK