Why this swap needs three times as much
Baking soda is pure sodium bicarbonate — a base with no acid of its own, so it only produces lift when a recipe's own acidic ingredient reacts with it. Baking powder already has both a base and a powdered acid built in, and that mix is diluted with cornstarch to keep it stable on the shelf, so it's a much weaker leavener by volume. Using about three times as much baking powder makes up for that dilution.
The catch: the recipe's original acid goes unused
This is the part that makes it an imperfect swap rather than a clean one. If a recipe uses baking soda, it's almost always because something else in it — buttermilk, brown sugar, cocoa powder, yogurt, molasses — is acidic, and the soda is there specifically to neutralize that acid while also producing lift. Swap in baking powder instead and that acid is left unreacted, which can leave a faint tangy or sour edge in the final flavor. It's a fine emergency fix, but not a substitute to reach for as a first choice if real baking soda is an option.
FAQ
What if my recipe has no acidic ingredients at all? Then this swap won't work — baking powder still needs its own moisture to activate, but without any additional acid to neutralize, you may notice a slightly metallic or bitter aftertaste from the extra powder. In that case, a trip to the store beats this substitute.
Does the reverse direction (out of baking powder, only have soda) work the same way? No — that's the opposite swap, rebuilding baking powder's missing acid component with cream of tartar, lemon juice, vinegar, or buttermilk.See our baking powder substitute calculatorfor those ratios.