Butter to Oil Converter

You are halfway through a cake and the butter is gone. Swapping in the same weight of oil gives you a heavy, greasy batter, because butter carries water and oil is pure fat. The kitchen rule is three quarters: 100 g of butter becomes 75 g of oil. Enter the amount, pick the direction, and the tool runs it both ways, always in grams.

What the ratio does not give back is the water. Butter runs around 80% fat and 16% water, so dropping 100 g of it also removes about 16 ml of liquid the recipe was counting on. In drier batters, a tablespoon or two of milk covers the gap. One more thing that trips people up: the answer comes in grams, while oil at home is measured by volume. At a density near 0.92 g/ml, those 75 g are about 81 ml.

The swap behaves well in simple cakes, muffins, brownies and sandwich bread. It fails wherever solid fat is the structure: puff pastry, shortbread, sablé dough, buttercream, and anything that starts by creaming butter with sugar, since oil holds no air. Margarine ranges from 60% to 80% fat depending on the brand and does not fit this factor. Everything is computed in your browser.