Projectors are important display devices for large scale augmented reality applications. However, precisely calibrating projectors with large focus distances implies a trade-off between practicality and accuracy. People either need a huge calibration board or a precise 3D model [12]. In this paper, we present a practical projector-camera calibration method to solve this problem. The user only needs a small calibration board to calibrate the system regardless of the focus distance of the projector. Results show that the root-mean-squared re-projection error (RMSE) for a 450cm projection distance is only about 4mm, even though it is calibrated using a small B4 (250 × 353mm) calibration board.