This paper presents an object volume measurement system on a conveyor belt. A client-server architecture is proposed to obtain a flexible and efficient measurement system for object size on the conveyor belt. The client works to integrate the sensor data and convert them into three dimensional point cloud. The server is responsible for calculating the object size. A laser scanner scans the object on the conveyor belt that moves with a constant speed. We applied the trigonometric function method to integrate two-dimensional distance data form the laser scanner and encoder data of the conveyor belt to obtain three-dimensional point cloud data. A progressive morphological filter was adopted to segment the background point cloud and the object point cloud. Then a convex hull algorithm was applied to find the set of the smallest convex polygon that contains all the object point cloud. Further, we can find a rectangle which has the smallest area to determine the object size. The experimental results show that the shape of object can be square, cylindrical or irregular. When the conveyor belt speed is set at 20 cm/s, the percentage error of the object size measurement is around 5% with the laser scanner installed at 50 cm above the conveyor belt and that within 7% with the laser scanner installed at 100cm.