Most of the calibration methods proposed for the Stewart platform require complex computation or low noise data for the platform's accuracy to be determined. They are not suitable for practical use in a production environment, where the measurement and calibration method should be simple and robust. Using an external laser measuring device to determine the actual accuracy of a Stewart platform, a practical and simple leg length compensating calibration method, that improves the accuracy of the Stewart platform by a magnitude of around 7, is proposed. The procedures and computation algorithms of the calibration method are shown.