Hong Kong catty (司馬斤) to kilograms
Convert Hong Kong catty (司馬斤) to kilograms. One catty is 604.78982 g by law — not 600 g, and not 500 g.
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The formula
kilograms = catty × 0.60478982The figure is exact and statutory. Hong Kong’s Weights and Measures Ordinance fixes one catty at 604.78982 grams — an oddly precise number because it was derived from the older 司馬 standard and then pinned to the metric system, rather than being rounded to a convenient one.
Three catties, and Hong Kong’s is none of the round ones
| Name | Grams | Where |
|---|---|---|
| 司馬斤 | 604.78982 | Hong Kong, Macau |
| 台斤 | 600 | Taiwan |
| 市斤 | 500 | mainland China |
Hong Kong’s is 0.8% heavier than Taiwan’s and 21% heavier than the mainland’s. The gap against Taiwan is small enough to ignore at a market stall and large enough to matter in a wholesale contract; the gap against the mainland is large enough to matter anywhere.
See 台斤 to kg for the Taiwanese unit.
Quick reference
| Catty | Kilograms | Grams |
|---|---|---|
| 0.5 斤 | 0.302 kg | 302.4 g |
| 1 斤 | 0.605 kg | 604.8 g |
| 2 斤 | 1.210 kg | 1209.6 g |
| 3 斤 | 1.814 kg | 1814.4 g |
| 5 斤 | 3.024 kg | 3023.9 g |
| 10 斤 | 6.048 kg | 6047.9 g |
| 100 斤 | 60.479 kg | 60,479 g |
Taels
A catty is sixteen taels (兩), so a Hong Kong tael is 37.79936 g:
| Unit | Grams |
|---|---|
| 1 司馬斤 | 604.78982 |
| 1 兩 (⅟₁₆ catty) | 37.79936 |
| 1 錢 (⅒ tael) | 3.77994 |
| 1 分 (⅒ mace) | 0.37799 |
The tael and the mace are still the working units in Chinese medicine dispensaries and in the dried-seafood trade, where prices per tael are the norm.
Gold is different. Hong Kong’s gold market trades in a tael of 37.429 g — the troy tael — which is not the same as the 37.799 g tael used for goods. A quoted “tael of gold” is the smaller one. This is the same class of trap as the troy ounce.
Where it is still used
Hong Kong law permits both metric and imperial-and-Chinese units in trade, and wet markets, dried-goods shops and traditional medicine dispensaries almost universally price per catty or per tael. Supermarkets price per kilogram or per 100 g.
| Per catty | Per kg |
|---|---|
| HK$20 | HK$33 |
| HK$40 | HK$66 |
| HK$60 | HK$99 |
| HK$100 | HK$165 |
A price per catty looks about 40% cheaper than the same figure per kilogram, purely because the unit is smaller.
Estimating in your head
Multiply by 0.6. The error is 0.8%, which is smaller than the difference between the Hong Kong and Taiwanese catties in the first place. For anything where 0.8% matters, use the statutory figure.