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How to double a recipe without ruining it

Doubling a recipe sounds simple: everything times two. For most ingredients, that's exactly right. But anyone who has watched a doubled cake collapse knows there's a little more to it. Here's what actually matters.

The base rule: scale factor 2

Doubling means multiplying every quantity by a factor of 2. 200 grams of flour becomes 400 grams, 1½ cups of milk becomes 3 cups, and ¾ teaspoon of cinnamon becomes 1½ teaspoons. For main ingredients — flour, meat, vegetables, liquids — you can follow this rule blindly; precision pays off here.

The fiddly part is fractions. Half the mental math in doubling comes from measures like 1 1/3 tablespoons or ⅛ teaspoon. Our recipe scaler does that arithmetic automatically and rounds to practical kitchen measures.

The exceptions: leavening and salt

Baking powder, baking soda and yeast don't scale neatly. In a double batch, leavening works more efficiently than in a single one, and double the yeast can make a dough rise too fast and too wildly. The rule of thumb: when doubling, use roughly 1.5 times the original amount of leavening, and watch the dough rather than the clock.

Salt behaves differently too. Flavour doesn't scale perfectly with volume: start with about 75% of the calculated amount, taste, and add as needed. You can always add salt — you can't take it out.

Cooking times don't double

A common mistake: doubling the oven or stove time along with the ingredients. It's almost never needed. A double pot of soup simmers only slightly longer than a single one, and a double batch of cookies bakes the same time per tray. What does matter is thickness. Pour a double batter into the same pan and the layer is twice as deep — that changes the baking time dramatically. Use two pans, or bake in two rounds.

Practical tips when doubling

• Use a bigger pot or bowl. A double volume needs room to stir, rise and bubble.
• Bake in two pans rather than one overfilled one — more even results, predictable timing.
• Taste as you go. Spices, acid and heat can be scaled slightly conservatively in large batches.
• Write down or print the new quantities so you're not doing math with floury hands halfway through.

With these adjustments, you can double almost any recipe without trouble — from pasta sauce to banana bread.