We study the rotation characteristics and the mechanism to produce the acoustic torque for polymer thin-film acoustic rotors levitated in ambient air in a 40 kHz ultrasound standing wave. It was found that the polymer thin-film disk can be efficiently rotated by attaching short blade around, of which shape can control the direction of the rotation. We further demonstrated that miniaturized acoustic rotors down to 25 μm in diameter can be rotated in liquid by in-plane standing wave produced by 2-10 MHz ultrasound. Our study will pave the way for further optimization of acoustic rotors as sample holders for experiments that demand sample rotation and the exploration of micron-scale acoustic rotors in liquid.