If you ever plan on cooking, you'll definitely need to know how to convert cups to milliliters (mL) and mL to cups. Recipes don't always measure things the way that's easiest for you, so knowing how to convert can be helpful.
Differentiate between fluid measures and dry measures. Cups can be used to measure both fluid and dry ingredients, but milliliters are a fluid measurement. If you wanted to convert a cup of flour, for example, you'd need to convert to grams, not mL.
Determine how many cups you need for the recipe. It's actually easier to do the conversion using the entire amount needed than it is to figure out how many mL in a cup and then multiplying it again.
Convert cups to ounces. Though it may seem simpler to just multiply the number of cups to get the answer, if you have a recipe that calls for 2 1/2 cups of milk, then it's simpler to be dealing with whole numbers instead of fractions. One cup is 8 oz., so the equation is: 2.5 cup x 8 = 20 oz.
Use the number of ounces to convert your liquid measurement to mL. One ounce is equal to 29.57 mL. For practicality's sake, it's better to round this up to 30 and multiply the number of oz. by a whole number. So, using the information from Step 3, the equation would look like so: 20 oz. x 30 = 600 mL