A koku (石) is a quantity of rice, historically defined as enough rice to feed one person for one year, then as 180.39 liters, or about 5 bushels (48 gallons).
During the Edo period of Japanese history, each han had an assessment of its wealth, and the koku was the unit of measurement. The smallest han was 10,000 koku and the largest (other than the Shogun) was called "a million koku domain". Many samurai, including hatamoto, received stipends in koku while few received salaries instead. In the Tohoku and Hokkaido domains where rice could not be grown, these han's economy were still measured by koku but they were not adjusted from year to year. Thus some han had larger economy than their koku indicated which let them use to fund development projects.
Koku was also used to measure how much a ship could carry when all its loads were rice. Smaller ships carried 50 koku while the biggest ships carried over 1,000 koku. The biggest ships were actually larger than military vessels owned by the shogunate.
In the Meiji period, the koku measurement was abolished and the metric system was installed.
The Hyakumangoku Matsuri (festival) in Kanazawa, Japan celebrates the city's rice production reaching 1,000,000 koku.