Replacing butter with oil can make cakes and quick breads softer for longer, but it removes water, milk solids and the solid structure that butter provides. A successful swap needs both the right amount and the right recipe.

How much oil replaces butter?

For an exact fat match, multiply the butter weight by 0.80. One hundred grams of butter contains roughly 80 g fat, so use 80 g oil. The common kitchen shortcut is to use three-quarters as much oil by volume.

Use the butter to oil converter for grams, millilitres, cups or tablespoons. Exact mode conserves fat; Quick mode gives the familiar 0.75 rule.

Replace some of the missing water

Standard butter is about 16–17% water. Oil has essentially none. In a cake or muffin, add roughly one tablespoon of milk or water for each 100 g butter replaced if the batter appears unusually thick or the recipe has little other liquid.

Do not add that moisture blindly to every recipe. Fruit purees, yoghurt, sour cream and eggs may already provide enough water. Compare the batter with the consistency the recipe describes.

Recipes where oil works well

  • Muffins and quick breads mixed by the two-bowl method
  • Carrot, chocolate and spice cakes
  • Brownies where a softer chilled texture is desirable
  • Banana bread and fruit-rich loaves
  • Bakes intended to stay moist for several days

Use a neutral oil such as vegetable or canola unless the recipe suits olive or coconut flavour. The vegetable oil guide explains the neutral baseline, while the olive oil guide covers its stronger character.

Recipes where oil is not equivalent

Do not make a simple substitution in croissants, puff pastry, shortbread or biscuits that depend on pieces or layers of solid butter. Oil cannot create laminated layers or hold the same shape.

Creamed cakes also need care. Butter and sugar trap air during creaming; pouring oil into the mixture removes that mechanical leavening. A recipe can be redesigned around oil, but the ratio alone cannot preserve the method.

Expect a different result

Oil generally makes the crumb feel moister and more flexible. Butter gives more dairy flavour, browning and firmness when cool. Neither is universally better. Choose the fat whose physical behaviour supports the bake, then use the converter to get the quantity right.