【How-to】How many milliliters in an ounce

So, a milligram is a thousandth of a thousandth of a kilogram, and a milliliter is a thousandth of a liter. Notice there is an extra thousandth on the weight unit. Therefore, there must be 1,000 milligrams in a milliliter, making the formula for mg to ml conversion: mL = mg / 1000 .