As a recent technological development, high-speed atomic force microscopy (AFM) has provided unprecedented insights into dynamic processes on the nanoscale, and is capable of measuring material property variation over short timescales. Miniaturized cantilevers developed specifically for high-speed AFM differ greatly from standard cantilevers both in size and dynamic properties, and calibration of the cantilever spring constant is critical for accurate, quantitative measurement. This work investigates specifically, the calibration of these new-generation cantilevers for the first time. Existing techniques are tested and the challenges encountered are reported and the most effective approaches for calibrating fast-scanning cantilevers with high accuracy are identified, providing a resource for microscopists in this rapidly developing field. Not only do these cantilevers offer faster acquisition of images and force data but due to their high resonant frequencies (up to 2 MHz) they are also excellent mass sensors. Accurate measurement of deposited mass requires accurate calibration of the cantilever spring constant, therefore the results of this work will also be useful for mass-sensing applications.