Fetching details from the dictionary...

koku; traditional unit of volume, approx. 180.4 litres
measure of a Japanese-style boat's loading capacity (approx. 278.26 liters)
「石」 has other readings with different meanings.
百石の米を貯蔵する。
Store one hundred koku of rice.
昔は米を石で量っていました。
In the old days, rice was measured in koku.
この藩は五万石の領地があった。
This domain had territory worth 50,000 koku.