Baking Soda vs Baking Powder

• Baking soda (sodium bicarbonate) needs an acid in the recipe — buttermilk, yogurt, brown sugar, cocoa, lemon.
• Baking powder = soda + dry acid (+ starch); usually double-acting.

Substitutions

• For 1 tsp baking powder: ¼ tsp baking soda + ½ tsp cream of tartar.
• For 1 tsp baking soda: about 3 tsp baking powder (flavor and salt change slightly).

1 tsp baking powder weighs about 4 g — see baking powder conversions.