I started farming for the 2014 today. I am spraying the fields with Roundup to control weeds before I work the fields before planting. Today it was a little windy in the early afternoon, but this evening I was able to spray about 50 acres. Here is tha math for figuring the acres covered in a hour. I am going 5.5 miles an hour and the sprayer is 75 feet wide. An acre is 43560 square feet. So every mile the sprayer covers 396000 square feet or 9.10 acres. 5.5 mph times the 9.10 says I cover 50.5 acres each hour. As a farmer you use these caculations all the time. Next time I will cover application rate caculations.