What is a cun in acupuncture and shiatsu

A cun (sometimes written tsun) is not a fixed centimetre. It is a unit proportional to the body of the person you are studying. The same “three cun” fits a short forearm and a long one: the reference travels with the body, not with a shop ruler.

What it is for

Classical texts locate points with bones and cun: “three cun below the knee”, “one and a half cun from the spine”. Without that measure, a sheet is only a name. With it, a student can check the landmark on the body and in the 3D atlas. It is for study. It does not say which point “should be pressed”.

Two forms people mix up

Thumb cun. The width of that person’s thumb interphalangeal joint is often taken as one cun. It is quick in class. It does not replace bone: if the text says “beside the tibial crest”, the bone leads. Proportional cun. A known segment is divided (classically, elbow crease to wrist crease is 12 cun) and shared out. It is more faithful for long distances on the arm, leg or back. One-finger, three-finger and four-finger cun are shortcuts of the same idea: they compare with that person’s hand, not with yours if you are measuring someone else.

Study examples

ST36 (Zusanli): about three cun below the lower border of the patella, one finger lateral to the tibial crest. Open /points/st36 and confirm the landmark on /explore/body, not only the number. LI4 (Hegu): on the dorsum of the hand, toward the midpoint of the second metacarpal. Cun helps little here; bone leads. A good atlas mixes measure and bony reference. Back shu line: the inner Bladder line is studied one and a half cun from the midline. BL23 and its neighbours make sense with that distance and the vertebra, not with a bare figure.

Common mistakes

Measuring someone else’s body with your own fingers. The cun belongs to the body being studied. Converting cun into “universal” centimetres. That table breaks the proportion. Memorising the number and skipping the bone. Cun orients; the landmark confirms. Using the measure as a clinical protocol. Locating on the map is not prescribing a treatment.

How to practise it on Meridiania

1) Read the sheet (ST36, LI4 or a back shu). 2) Note cun plus bone in the notebook. 3) Rotate the body on /explore/body and mark the region. 4) Repeat on /practice/drills/locate until number and bone agree. 5) Cross-link the meridian, not a list of “what it is for”.

Location study on meridiania.net — not medical advice and not a substitute for your school.