Convert Qian/Mace to pounds

Two systems, one character

Mainland China redefined the jin at exactly 500 grams and the liang at one tenth of that, so the mainland qian is exactly 5 grams. Hong Kong kept the older sixteen-tael catty of 604.78982 grams, which makes the Hong Kong liang 37.799 grams and the qian 3.7799 grams. The written character is identical in both places.

This is the single largest source of error involving the unit. A prescription written in Guangzhou and dispensed in Hong Kong, or a gold weight quoted across the border, differs by a factor of about 1.32 if the wrong system is assumed. Nothing in the number itself signals which system applies — only the jurisdiction of the document does.

The pharmacy unit

Traditional Chinese medicine prescriptions are written in qian and liang, and dispensaries across the mainland, Hong Kong, Taiwan, Malaysia and Singapore still weigh to them. Classical formulae inherited from Han and Ming texts use the unit too, but with the historical values of their own period, which were considerably smaller than either modern figure.

Practitioners handle this by treating classical dosages as proportions rather than absolute masses, and by rescaling the whole formula to a modern qian. Anyone converting a historical text for research purposes should preserve the ratios and state explicitly which modern value was used to anchor them, rather than presenting a single gram figure as if it were the original intent.

Gold, pearls and small metalwork

Jewellers use the qian for gold chain, small castings and setting stones. In Hong Kong the chain runs tael, mace, candareen and cash, each a tenth of the one above, giving a decimal ladder from 37.799 grams down to about 37.8 milligrams. That decimal structure is why the mace survived alongside the metric gram: it is easy to compute with mentally, unlike the sixteenths that connect the tael to the catty.

The pearl trade historically used the same ladder, and older auction catalogues quote pearl weights in mace rather than grains or carats. Converting those catalogues requires the Hong Kong value, since the trade was centred there, and the resulting carat figures should be treated as approximate because historical pearl weighing was not held to modern gemmological tolerances.

Dispensing and documentation

A dispensary weighing to the qian is working to a tenth of a liang on a beam balance, and the practical resolution of that measurement is coarser than the difference between many published herb dosages. This is why traditional prescriptions specify proportions and a total decoction volume rather than relying on absolute masses alone.

For documentation — customs declarations, research papers, export labelling — the useful practice is to record both the qian figure and its gram equivalent with the system named. 'Three qian (Hong Kong, 11.34 g)' is unambiguous; '11.34 g' alone loses the clinical intent, and 'three qian' alone is a 32 percent question mark.

Common mistakes to avoid

• The mainland qian is exactly 5 g; the Hong Kong qian is 3.7799 g — a 32% difference with no visual marker in the text.
• Classical medical texts use period values much smaller than either modern figure; treat them as proportions.
• Mace, candareen and cash form a decimal ladder, but the tael-to-catty step is sixteenths — do not assume decimal throughout.
• Historical pearl and gold catalogue weights were not measured to modern tolerances; converted figures inherit that uncertainty.

Questions people ask about the Qian/Mace

How many grams is one qian (mace)?

In mainland China, exactly 5 grams. In Hong Kong, 3.7799 grams, because Hong Kong retains the older sixteen-tael catty of 604.78982 g. Always establish the jurisdiction before converting.

Why do Chinese medicine prescriptions still use qian?

Dispensing practice, teaching texts and classical formulae are all written in qian and liang, so the unit stayed in clinical use even after metrication. Dispensary scales in Hong Kong and Southeast Asia are graduated in it.

Is mace the same as qian?

Yes. "Mace" is the English trade name used in Hong Kong and Straits commerce for the Chinese qian, one tenth of a liang or tael.