Baking soda vs. baking powder: what is the difference?

How baking soda works

Baking soda (sodium bicarbonate) is a pure base. On its own, it does nothing. It needs an acid in the recipe to activate — buttermilk, lemon juice, vinegar, yogurt, cocoa powder, or brown sugar all work. When soda meets acid, it produces carbon dioxide bubbles immediately, which make the batter rise.

Because the reaction starts instantly, batters with baking soda need to go straight into the oven. Waiting causes the bubbles to escape before they set in the heat.

Baking soda is about 3–4 times stronger than baking powder. Too much of it leaves a metallic, soapy aftertaste. Always weigh it — one cup of baking soda weighs 220 grams, but most recipes use it in teaspoon quantities where precision is essential.

How baking powder works

Baking powder is baking soda with a dry acid (cream of tartar or sodium aluminium sulfate) and cornstarch already mixed in. It is "double-acting" — the first reaction happens when it gets wet, the second when it gets hot. This gives you more flexibility: the batter can sit briefly before baking.

Baking powder is used in recipes that do not contain an acid. Recipes with acidic ingredients — like those with buttermilk or lemon juice — typically use baking soda instead, or a combination of both.

Can you substitute one for the other?

In an emergency, you can substitute baking powder for baking soda using three times the amount (e.g. 1 tsp soda → 3 tsp powder). The result will be slightly different in flavour and texture. Going the other way is harder: replacing baking powder with soda requires adding an acid to the recipe, which changes everything else.

Cream of tartar is often used alongside baking soda as the acid component — ¼ tsp cream of tartar per ¼ tsp baking soda is roughly equivalent to 1 tsp baking powder.