we got this formula from the salesman we purchase our chemicals from: 1. measure out 204 ft. 2. time yourself driving the distance in the same gear and at a constant rpm 3. use water and one nozzle run your sprayer at that rpm you drove the 204 ft into a container the same amount of time it took you to drive it(will need to measure amount of water sprayed into the container) take the number of ounces that comes out of the nozzle times the number of nozzles on your boom ( this will give you the total ounces being sprayed) 4. ounces equals gals sprayed per acre !!! lets say for example: 4 ounces came out of the nozzle,run at the determined amount of time multiplied by the number of nozzles on the boom.. lets say four nozzles on boom...4x4=16 total ounces...ounces equal gal. per acre, so you are spraying 16 gal. per acre. so at the gear and rpm you determined to spray at, on your 4 nozzle boom will put down 16 gal. per acre. we are not rocket scientists and I`m sure our travel time is not exact but we get close and this formula has worked well for us...good luck!