1 Kings 18:31-32

31Elijah took twelve stones, one for each of the tribes descended from Jacob, to whom the word of the LORD had come, saying, “Your name shall be Israel.” 32With the stones he built an altar in the name of the LORD, and he dug a trench around it large enough to hold two seahs That is, probably about 24 pounds or about 11 kilograms of seed.