What Is the Difference Between Baking Powder and Baking Soda?

They sit next to each other in almost every pantry, look nearly identical, and get used interchangeably by mistake more often than any other baking ingredient. But the difference between baking powder and baking soda is real, and mixing them up can leave a cake flat, a cookie metallic-tasting, or a batch of biscuits that never rise.

The Short Answer

Baking soda is pure sodium bicarbonate – a base that needs an acid to react and produce the gas bubbles that make baked goods rise. Baking powder already contains both an acid and a base (usually cream of tartar plus baking soda, along with cornstarch to keep it dry and stable), so it can leaven a recipe on its own without any extra acidic ingredient. That single distinction – needs an acid vs. already has one – explains almost every practical difference between the two.

What Baking Soda Actually Does

On its own, baking soda does nothing but sit there. It only starts producing carbon dioxide once it touches something acidic – buttermilk, yogurt, brown sugar, cocoa powder, honey, or lemon juice are all common triggers in recipes. If a recipe uses baking soda but doesn’t include enough acid to react with, you’ll often notice a faintly metallic or soapy aftertaste, which is unreacted baking soda left behind in the finished bake.

What Baking Powder Actually Does

Most baking powder sold today is “double-acting,” meaning it reacts twice: once when it gets wet, as the batter is mixed, and again when it hits oven heat. That second reaction is what gives baked goods a more reliable, even rise, since the batter keeps getting lift even after it’s poured into the pan and sitting for a few minutes. Because baking powder already includes its own acid, it doesn’t depend on anything else in the recipe to activate.

Why Some Recipes Use Both

Recipes that include acidic ingredients – like buttermilk pancakes or chocolate cake – often still call for baking powder alongside baking soda. That’s because the acid in the recipe may only be enough to neutralize the baking soda’s flavor and give a small amount of lift, not enough to fully leaven the batter. The baking powder fills in the rest of the rise the recipe needs.

Can You Substitute One for the Other?

Not directly – baking soda is roughly three to four times stronger than baking powder by volume, and it needs an acid the recipe may not otherwise have. In a pinch, you can replace 1 teaspoon of baking powder with 1/4 teaspoon of baking soda plus 1/2 teaspoon of cream of tartar, which mimics what’s already inside store-bought baking powder. Going the other direction – using baking powder in place of baking soda – usually requires three times as much and can leave a recipe tasting slightly bitter or chalky.

How to Tell If Yours Still Works

Both lose potency over time, usually within six months to a year of opening. To test baking soda, add a small spoonful to vinegar – it should fizz immediately and vigorously. To test baking powder, stir a spoonful into hot water instead; the same immediate fizz means it’s still active. If either barely reacts, it’s time to replace it, since weak leavening is one of the most common reasons a cake or batch of cookies doesn’t rise properly.