How to convert amounts of butter into oil?
Now that we understand the composition of both fats, it becomes obvious that in order to replace butter with oil, we need to subtract 20% of the total weight. So for example, if we need to replace 3,5 oz. of butter with oil, 2,8 oz. of oil will be necessary (3,5 oz. - 20% of the total).
Butter must be replaced with oil in this way when dealing with small amounts, like when preparing a cake, for example.
When preparing for lots of people and quantities increase, the correct replacement of butter with oil also requires the addition of the amount of water present in butter. So, for 35,3 oz. of butter in a recipe, in addition to 28,2 oz. of oil, it is also best to add 7,1 oz. of water, to rebalance the liquid to solid ratio.