Abstract: A calibrating device for agricultural sprayers utilizes an elongate, flexible throw-away bag of plastic sheet material having a top portion adapted for attaching to an agricultural sprayer boom and an open interior cavity for collecting the spray from a sprayer dispenser nozzle. A facing wall of the bag has a plurality of indicia thereon to measure the rate of spray for calibration of the nozzles to a correct application setting. The indicia include transverse marks indicating quantity, such as gallons, and longitudinal lines indicating rate.