A mathematical model is derived to predict the maximum speed of a focused laser beam in the laser cutting of thin materials. This model contains only two material parameters and is used to obtain an explicit relationship between the cutting speed and laser parameters. The model shows that there exists an optimal focal spot radius with which cutting speed is maximized for a given laser power. We compare the modeling results with experiments and find a good agreement after correcting laser fluence. This work is useful for the practical application of lasers in processing thin materials such as sheets and panels.