Baking Soda and Baking Powder: Swap Rules

Baking soda is pure sodium bicarbonate and releases gas only when it meets an acid, while baking powder is a ready-made blend that carries its own acid. That is why one can sometimes stand in for the other: Arm & Hammer and King Arthur Baking both point to three times as much baking powder when a recipe calls for baking soda. Going the other way takes baking soda plus an acid, and McGill University's Office for Science and Society notes that both substitutions might alter taste and texture slightly.

What is baking soda, and why does it need an acid?

Baking soda is sodium bicarbonate, a base, and it only produces rising gas when an acid is present to react with it. Dickinson College's Chemistry in the Kitchen blog describes it as a base with a pH above 7. Arm & Hammer calls it a "single ingredient leavener that needs an acid to work."

When the acid and the base meet, the reaction produces carbon dioxide. According to Dickinson College, that gas creates air pockets in cookie dough and increases its volume. Without an acid in the recipe, the soda has nothing to react with and the batter stays dense.

What is baking powder, and why does it work without an acid?

Baking powder works alone because the acid is already inside it. According to Arm & Hammer, it combines baking soda with at least one acid ingredient and a stabilizer such as cornstarch. McGill University puts it as sodium bicarbonate combined with a powdered acid.

America's Test Kitchen states that baking powder leavens without acidic ingredients. Mixing it into a wet batter brings the dry acid and the soda together, and the gas starts to form.

What does double-acting baking powder mean in practice?

Double-acting powder produces gas in two stages instead of one. King Arthur Baking says grocery stores often stock "double-acting" baking powder, which reacts twice.

The first stage starts at mixing. University of Illinois Extension says the first leavening happens when the powder meets wet ingredients. King Arthur Baking places the second reaction "when the batter hits the heat and begins to bake." America's Test Kitchen summarizes it the same way: first by moisture, then by heat.

Can you swap one for the other, and in what amounts?

Yes, with different rules in each direction. The table compares the swaps as published on each page on 31/10/2026.

University of Illinois Extension words the first swap cautiously, saying you could try tripling the amount of baking powder. Baking soda alone cannot replace baking powder, because McGill University explains that baking soda must be supplemented with an acid. Cream of tartar plays that role in the table above.

Why do some recipes use both?

The two ingredients do different jobs, and America's Test Kitchen notes that many recipes call for both. Baking soda reacts with the acid already in a recipe and, as the next section shows, pushes browning. Baking powder adds lift that does not depend on that acid. A recipe with some acidic ingredient but not enough to lift the whole batter can use soda for the first job and powder for the second.

How does baking soda change browning, flavor and crumb?

Baking soda deepens browning because it makes a dough or batter more alkaline. America's Test Kitchen gives that as the reason baking soda increases browning in doughs and batters. Dickinson College adds that an excess creates an alkaline environment that speeds up the Maillard reaction, the browning chemistry behind crust and toasty flavor.

Crumb follows the gas. The carbon dioxide from soda and acid opens air pockets, per Dickinson College. In a cornbread comparison, America's Test Kitchen reports that the loaf leavened only with baking powder came out bright yellow with an open crumb.

How can you tell whether they still work?

A quick fizz test works for both. King Arthur Baking, in a page published 05/11/2015, describes it:

1. For baking soda, stir 1/2 teaspoon into an acid. The mixture should fizz immediately and quite vigorously.
2. If the fizzing is gentle or minimal, the same page says it is time to buy a new carton of baking soda.
3. For baking powder, put 2 tablespoons of warm water in a bowl and stir in 1/2 teaspoon of the powder, then watch for the same kind of bubbling.

Why do bakes taste metallic or soapy, and how do you avoid it?

Too much leavener, or too little acid to match it, is the usual cause. University of Illinois Extension warns that too much baking soda without enough acid can give a metallic taste. Dickinson College says the soapy taste comes from excess baking soda left over after the reaction.

Powder can cause trouble too: America's Test Kitchen found its baking-powder-only cornbread tasted sour and metallic. Level measuring and following the leavener the recipe names are the practical safeguards. When a swap is unavoidable, use the ratios in the table and expect a small change in flavor and texture.

How do the two compare side by side, source by source?

The table below puts the sources next to each other, so you can see where they agree and which page backs each point. Dates are publication dates where the page gives one; otherwise the page was read on 31/10/2026.

If you rely on a single brand, the answer from Arm & Hammer is that, according to the brand, baking powder is a blend of baking soda, one or more acid components and a stabilizer like cornstarch, and baking soda should be replaced with 3x the amount of baking powder, as stated on its page in October 2026. The same ratio appears on King Arthur Baking's page, so the swap does not depend on which brand's advice you follow.

Sources

• Baking Powder versus Baking Soda, Arm & Hammer (Church & Dwight Co., Inc.), consulté le 31/10/2026
• What's the difference between baking soda and baking powder?, King Arthur Baking, consulté le 31/10/2026
• How to test yeast, baking powder, and baking soda for freshness, King Arthur Baking, consulté le 31/10/2026
• Baking Soda vs. Baking Powder, University of Illinois Extension, consulté le 31/10/2026
• Baking Soda vs. Baking Powder, America's Test Kitchen, consulté le 31/10/2026
• The Science Behind Baking Soda, Dickinson College, Chemistry in the Kitchen, consulté le 31/10/2026
• What's the Difference Between Baking Soda and Baking Powder?, McGill University, Office for Science and Society, consulté le 31/10/2026