It is generally accepted that one cup of melted butter is equivalent to a three-fourths cup of oil. If you need 1 2 cup oil, you can try measuring a little more than one of melted butter or less than 3/4 cup of oil. Are various other conversions between and oil that may be, such as replacing 1/ cup of butter with 14 cups of oil or 1/2 cup of butter with/3 a cup of oil. You should also note that different types have different flavor profiles and benefits, so if you looking for a certain flavor or health benefit, it may be best to use the best type of oil in your recipe.