When measuring the size of industrial liftgate, it is important to confirm the width, height and wall thickness of the door opening. In order to maintain the accuracy of the measurement data, it is necessary to measure the width, height and wall thickness at least three times. When measuring the height of the door opening, take the left, middle and right points as the benchmark, and the smaller height shall prevail; When measuring the width of the door opening, the upper, middle and lower points shall be measured respectively, and the smaller width shall prevail; When measuring the thickness of the wall, measure the upper, middle and lower points on the left and right walls respectively, subject to the large width.