In this study, we report a method to accurately calibrate the forces measured by a wearable device for measuring blood pressure pulse waves by the arterial tonometry method to obtain blood pressure measurements. A device based on the arterial tonometry method and a commercially available manometer was used for this research. The force and the blood pressure were simultaneously measured at three measurement heights using the arterial tonometry device and the manometer. The proposed calibration was found to reduce the influence of the inclination of the lower arm. As a result, the average coefficient of determination of the regression equations between the force and the blood pressure was 0.96. Thus, it was concluded that the proposed method can be used to accurately calibrate the measured forces to obtain blood pressure measurements with a high coefficient of determination.