One kilogram of water is equal to 500 ml of water. One kilogram = 500 grams, 500 grams = 500 ml, so one kilogram of water is equal to 500 ml of water. One kilogram is one kilogram. The two versions are different, but the meaning is the same. 1kg equals 1kg, two kilograms equals one kilogram, that is, 1kg equals 500g, and the density of water is 1g per cubic centimeter. According to the formula, mass is equal to density times volume.