In this article, a linear triaxial magnetometer calibration model with six observations is proposed for wearable inertial measurement unit (IMU) sensors. First, the information matrix of the six-parameter calibration model is derived under the proposed six-observation scheme, and its G-optimality is proven. Thereafter, a series of simulation studies were conducted to demonstrate the effectiveness and robustness of the six-observation scheme. Finally, the designed six-observation scheme is experimentally verified by the commercial IMU devices. The simulation and experimental results both demonstrate the efficiency and accuracy of the proposed optimal six-observation scheme. This scheme simplifies the calibration procedure and reduces the calculation workload, further providing guidance for the daily use of wearable sensor calibration.