A cun (寸) is not a fixed length. It is a proportion of the patient's own body, so "3 cun below the knee" lands in the same anatomical place on a child and on a tall adult. That is why a depth or distance in cun is never converted to millimetres on this site.
Bone-length (proportional) measurement
The primary method. Two landmarks are taken as a fixed number of cun apart, whatever the patient's size, and the distance between them is divided evenly. The scale descends from the bone measurements of the Ling Shu, refined by later practice, and is the basis of the modern international standard.
| Region | From — to | Cun |
|---|---|---|
| Head | Midpoint of the anterior hairline to midpoint of the posterior hairline | 12 |
| Head | Between the two corners of the frontal hairline (ST8 to ST8) | 9 |
| Head | Between the two mastoid processes | 9 |
| Chest and abdomen | Suprasternal notch to the xiphisternal junction | 9 |
| Chest and abdomen | Xiphisternal junction to the centre of the umbilicus | 8 |
| Chest and abdomen | Centre of the umbilicus to the upper border of the pubic symphysis | 5 |
| Chest and abdomen | Between the two nipples | 8 |
| Side of the trunk | Apex of the axilla to the free end of the 11th rib | 12 |
| Side of the trunk | Free end of the 11th rib to the prominence of the greater trochanter | 9 |
| Upper limb | End of the anterior axillary fold to the cubital crease | 9 |
| Upper limb | Cubital crease to the wrist crease | 12 |
| Lower limb | Upper border of the pubic symphysis to the medial epicondyle of the femur | 18 |
| Lower limb | Lower border of the medial condyle of the tibia to the tip of the medial malleolus | 13 |
| Lower limb | Prominence of the greater trochanter to the popliteal crease (level with the middle of the patella) | 19 |
| Lower limb | Popliteal crease (level with the middle of the patella) to the tip of the lateral malleolus | 16 |
| Lower limb | Tip of the lateral malleolus to the sole | 3 |
Finger measurement
A quicker approximation using the patient's fingers — not the practitioner's — since finger size is roughly in proportion with the rest of the body. Use it to find a point quickly, and fall back on the bone-length scale when the two disagree.
- Four fingers — 3 cun. Index, middle, ring and little fingers held together, measured across at the level of the dorsal crease of the middle finger's proximal interphalangeal joint. Most useful on the abdomen, the back and the lower limbs.
- Thumb — 1 cun. The width of the thumb across its interphalangeal joint.
- Middle finger — 1 cun. Bend the middle finger so its tip meets the pad of the thumb in a ring; the distance between the radial ends of the two interphalangeal creases on the middle finger is 1 cun. Suited to measuring along the limbs and across the back.
Sources
- World Health Organization. WHO Standard Acupuncture Point Locations in the Western Pacific Region. Manila: WHO Western Pacific Regional Office, 2008.
- Guo Changqing (ed.). Acupuncture of Acupoint Combinations: Quick Lookups. Heart Space Publications, 2020, chapter 1.