The conversion of ounces (oz.) to milliliters (mL) is a little bit tricky because it is a conversion from a measure of weight to a measure of volume. However, this conversion is simplified by the fact that you can use grams (g) as a go between. So, whether you are trying to figure out the metric volume of a substance for a recipe, or if you are just curious about how to switch between ounces and milliliters, there is an easy way to do so.
Accurately measure out the amount of substance that you are dealing with in ounces. For example, let's say that your material measures out as 16 oz.
Multiply the number of ounces of the substance in question by 28.35. This will give you the weight of the material in question in grams. If you multiply 16 by 28.35 you will get 453.6. This number is the number of grams that equals 16 oz.
Check the density of the material using a specific density chart, such as the one provided by K-Tek which can be found in the Resources section of this article. Write down the density of your substance, if it is water, for example, it will be given in the specific density chart as 1 g/cc (g/cc is the abbreviation for density). One cc (cubic centimeter) is equal to 1 milliliter, so the abbreviation for density could also be written as g/mL.
Divide the weight of your substance in grams by the density of that substance. This calculation will give you the volume of that substance in milliliters. So, if you are trying to find out the volume of 453.6 g of water, divide that number by 1 g/mL, which will show that the volume of 16 oz. (453.6 g) of water is 453.6 mL.
To help you keep all of the numbers involved in this conversion in proper order, consider writing out the conversion formula with words and then filling those positions in with the numbers with which you are working. For example to find the volume of 500g of dry ash you could write this formula: volume (mL) = weight (g) / density (cc/g); volume (mL) = 500 / 0.61; volume (mL) = 819.67.
Always be certain of just what the substance is that you are trying to find the volume of in milliliters. A specific density chart is useful because it gives you specific data, and so you need to be sure that you bring a specific substance to it; using a guess about what a substance is will give you an incorrect density and thus an incorrect volume in milliliters.