To replace butter with oil, use about 80g of oil for every 100g of butter — roughly three-quarters of the amount — and add a tablespoon of milk or water if the batter looks stiff. Butter is only about four-fifths fat; the rest is water and milk solids, which is why a like-for-like swap makes a greasy cake. Oil works beautifully in some bakes and poorly in others, and the difference comes down to whether the recipe relies on butter being solid.

The conversion

Weighing is more accurate than measuring by volume. If the recipe uses melted butter, the swap is at its most straightforward.

Bakes that work well with oil

• Loaf cakes and tray bakes — lemon drizzle, banana bread, gingerbread.
• Carrot cake and courgette cake — traditionally made with oil anyway.
• Muffins — the classic mix-wet-into-dry method was built for oil.
• Chocolate cake and brownies — oil gives a fudgy, even crumb.
• Olive oil or seed oil cakes where the oil's flavour is part of the point.

Oil cakes stay soft for longer than butter cakes, because oil stays liquid at room temperature while butter firms up. That's why an oil-based loaf often tastes better on day two.

Bakes that need butter

• Shortbread and many biscuits — they rely on solid fat for their snap and shape.
• Pastry — shortcrust, puff and rough puff need cold, solid fat to form layers.
• Croissants and laminated doughs.
• Classic Victoria sponge made by creaming — beating butter and sugar traps air. Oil can't do that, so use an oil-based sponge recipe instead of converting.
• Buttercream — no oil substitute gives the same texture.

Neutral oil or flavoured oil?

For a straight substitution where you want the cake to taste as the recipe intends, use a neutral oil such as high-oleic sunflower oil. If you're not sure what counts as neutral, see What Is a Neutral Oil?

Flavoured cold pressed oils open up a different kind of baking. Use them for part or all of the fat when the flavour belongs:

• Hazelnut oil with chocolate — brownies, chocolate loaf, a praline-style sponge. The pairing is hard to beat.
• Walnut oil with banana, carrot or coffee — banana bread and carrot cake both take it well.
• Poppy seed oil with lemon — see our lemon and poppy seed loaf.
• Pumpkin seed oil with spice — a small amount in a spiced pumpkin loaf gives a nutty, green note.

A good starting point is to replace a third to a half of the neutral oil with the flavoured one. Nut and seed oils are strong, and their delicate flavours soften in a hot oven, so you get a gentle background note rather than an overwhelming one. For the fullest flavour, brush a little of the oil over the warm cake or add it to a glaze.

A few tips for baking with oil

• Whisk the oil with the eggs and sugar first. It helps the oil emulsify so the crumb is even rather than greasy.
• Don't overmix once the flour goes in. Fold until just combined.
• Line the tin well. Oil cakes can be tender and a little fragile when warm.
• Expect a slightly flatter top. Oil batters are looser; a moderate oven helps them rise evenly.
• Use oil for greasing too. A thin brush of neutral oil and a dusting of flour releases a cake as well as butter does.

Storing oils you bake with

Nut oils are delicate: keep them in the fridge once opened and use them within a few months. A neutral, stable oil keeps happily in a cool, dark cupboard. Our guide to whether cooking oil goes off explains how to spot a tired bottle before it spoils a bake.

Frequently asked questions

How much oil do I use instead of butter?

About 80g of oil for every 100g of butter, roughly three-quarters of the amount. Add a tablespoon of milk or water if the batter looks stiff.

Can I use oil instead of butter in a cake?

Yes, in cakes made by mixing wet into dry ingredients — loaf cakes, muffins, carrot cake, chocolate cake and brownies. For creamed sponges, use a recipe written for oil rather than converting.

What bakes need butter rather than oil?

Shortbread, many biscuits, pastry, laminated doughs, creamed sponges and buttercream all rely on solid fat and don't work well with oil.

What is the best oil for baking?

A neutral oil such as high-oleic sunflower oil for a straight swap. For flavour, hazelnut oil suits chocolate, walnut oil suits banana and carrot cake, and poppy seed oil suits lemon.

Do oil cakes taste different from butter cakes?

With a neutral oil, the difference is mainly in texture: oil cakes are moister and stay soft for longer, while butter cakes have a richer, dairy flavour and a firmer crumb.

Can I bake with cold pressed nut oils?

Yes. Replace a third to a half of the fat with a nut or seed oil for a gentle background flavour, or brush a little over the warm cake for more.

The short version

Swap 100g butter for 80g oil in cakes, loaves, muffins and brownies; keep butter for pastry, shortbread and creamed sponges. Use a neutral oil like high-oleic sunflower for a straight swap, and try hazelnut or walnut oil when you want the oil to be part of the flavour.