Abstract Background To explore the difference between thumb and middle finger measurements and proportional bone measurements and identify the applicable parts of thumb and middle finger measurements in each part of the body. Methods A total of 394 healthy adults were enrolled. A high-precision electronic ruler was used to measure the lengths of their thumb and middle finger cun and the lengths of their bone proportional cun of the head–face, limbs, and trunk. The lengths of bone proportional cun were converted into a “1 cun ”, which were compared with the lengths of the thumb and middle finger cun . Results The thumb and middle finger cun are both commonly said to be “1 cun ” in length, but actual measurements revealed that the middle finger cun is significantly longer than that of the thumb cun ( P 0.05). The middle finger cun is generally significantly longer than the bone proportional cun ( q 0.05). Conclusion The middle finger cun is significantly longer than that of the thumb cun . The compatibility of finger cun measurements with the proportional bone standard varies by anatomical region. These findings provide an anthropometric basis for optimizing the selection of acupoint location methods in teaching and standardization. For educational purposes and in standard-body-type individuals, our data suggest that the thumb measurement might be prioritized in regions such as the head, face, and forearm, while the middle finger measurement may be more appropriate for areas such as the upper arm and lower leg, thereby balancing operational convenience with acupoint localization accuracy. Graphical abstract
Xian et al. (2026) studied this question.