Convert Koku (石) to millilitres

A volume that functioned as currency

One koku is one hundred shō, and a shō is 2,401/1,331 litres by the metric redefinition — giving a koku of about 180.39 litres. That exact-fraction basis, like the shaku, came from reconciling an existing standard with the metre rather than rounding it away.

Under the Tokugawa system, domains were rated by kokudaka: the assessed annual rice yield of their territory. A daimyō was a "hundred-thousand-koku lord" the way a modern company is described by revenue, and samurai stipends were paid in koku or in fractions of it. The unit measured volume and expressed political rank at the same time.

Why a volume and not a mass

Rice was measured by a standardised wooden box (masu) struck level, because volume measurement needed no balance and could be done in a village. The mass equivalent depends on the grain and its moisture — a koku of rice is roughly 150 kg — but the assessment system was built on the box, not the scale.

That is why koku figures in historical documents should be converted to litres first and to mass only with an explicit stated density. Going straight from koku to kilograms hides an assumption that varies by several percent with the crop.

Modern survivals

Sake production is still reported in koku by many breweries, and the industry's scale language — a brewery producing so many koku a year — descends directly from the rice measure that supplies the raw material. The shō and gō live on with it: a one-shō bottle (1.8 L) is the standard large sake bottle, and a gō (180 mL) is the standard serving.

Japanese timber uses a different koku, a volume of about 0.278 m³, for logs and sawn wood. The word is shared and the quantity is not, so a forestry document and a brewing document using "koku" are describing volumes that differ by a factor of more than a thousand.

Reading historical koku figures

Kokudaka assessments were political as much as agronomic: they were revised infrequently, and a domain's nominal koku could diverge substantially from its actual yield. Treat a kokudaka number as a rating, not as a harvest measurement, and say so when quoting it.

For any quantitative history, carry the koku figure and the litre conversion together, and state which koku — rice or timber — is meant. Both conventions appear in Edo-period and Meiji sources.

From tax assessment to timber

A koku is about 180.39 litres — the rice a person was reckoned to eat in a year — and Edo-period domains were ranked by their koku assessment rather than their acreage. A daimyō described as holding a hundred thousand koku was being described by tax yield, not by land area, and converting that figure to litres of rice tells you almost nothing about the size of the territory.

The unit outlived the tax system in two places. Japanese timber is still sold by the koku, redefined for wood as about 0.278 cubic metres, and sake brewers report annual production in koku. A bare koku figure therefore needs its commodity attached before conversion: rice volume and timber volume are different quantities sharing a name.

Common mistakes to avoid

• The timber koku (about 0.278 m³) is a different quantity from the rice koku (about 180.39 L) despite the shared name.
• Converting koku directly to kilograms hides a density assumption; convert to litres first and state the density used.
• Kokudaka ratings were administrative assessments, not measured harvests — do not read them as yield data.

Questions people ask about the Koku (石)

How many litres are in one koku?

About 180.39 litres — one hundred shō. A shō is about 1.8039 L, and a gō, the standard sake serving, is one-tenth of that.

How much rice is a koku in kilograms?

Roughly 150 kg, but this depends on grain and moisture. The koku is defined as a volume, so any mass figure carries a density assumption that should be stated.

What was kokudaka?

The koku rating of a Japanese domain under the Tokugawa shogunate — the assessed annual rice yield used to rank daimyō and to set samurai stipends and tax obligations.