An instrument has been designed to measure the rate of flow of air leaving any position on the surface of a bed of agricultural grain. A tapered tube and float meter is employed mounted on a collecting cone 9 in. in diam. and the range is 7-28 ft.3/min. per square foot of surface area. Calibration tests have shown that a common direct reading scale can be employed to give an accuracy of [plus or minus] 7% on airflow using all common farm grain.