You can use baking soda and cream of tartar instead of baking powder at a ratio of 1/4 tsp baking soda + 1/2 tsp cream of tartar per 1 tsp baking powder. That is the whole swap in one sentence, and it works because baking powder is baking soda plus acid, so the swap is always soda + an acid in the right ratio. Baking powder is not a single ingredient: it is baking soda mixed with a dry acid and a little starch, so whenever you replace it you have to rebuild that partnership yourself — soda for the lift, and an acid to wake it up. Get the ratio right and the cake rises exactly as the recipe intended. Get it wrong and you will taste it: too much soda leaves a soapy, metallic tang and a yellowish crumb, too little leaves a flat, dense bake.
This swap comes up most often at the worst moment — halfway through a recipe, with the oven already hot and the tin already greased. The good news is that the replacement is quick to measure and the chemistry is forgiving if you move fast. Leavening starts working the moment the soda meets the acid and the liquid, so once you have mixed the batter, get it into the oven without delay. The guidance below walks through the ratio in a table, three real recipes where the swap is used, what changes in the finished bake, and the cases where you should not substitute at all.
The ratio, in a table
| Baking powder called for | Baking soda | Cream of tartar |
|---|---|---|
| 1/2 tsp | 1/8 tsp | 1/4 tsp |
| 1 tsp | 1/4 tsp | 1/2 tsp |
| 2 tsp | 1/2 tsp | 1 tsp |
| 1 tbsp (3 tsp) | 3/4 tsp | 1 1/2 tsp |
| 2 tbsp | 1 1/2 tsp | 1 tbsp |
Measure the soda carefully — a quarter of a teaspoon looks like almost nothing, and it is easy to tip in twice as much by accident. Use proper measuring spoons, level them off with a knife, and do not guess with a dinner spoon. The ratio above is the sourced ratio for this pair: 1/4 tsp baking soda + 1/2 tsp cream of tartar per 1 tsp baking powder. All amounts in this guide are approximate, and the ratio comes from CookScale's substitution data rather than from a single brand's packaging. If the recipe matters — a cake for a celebration, a batch you are selling, or anything where a small error shows — weigh the ingredients on a kitchen scale and taste as you go.
One timing rule matters more than anything else with this swap. Baking powder is double-acting: it releases gas once when it meets liquid and again when it meets heat. Baking soda with an acid is mostly single-acting: the fizz starts as soon as the wet and dry ingredients meet. That is why a batter made with this substitute should go straight into a fully preheated oven. If you let it sit on the counter while you answer the door, a good share of the lift escapes into the air and no amount of extra baking time will bring it back.
Worked examples
Example 1: A vanilla sponge that needs its lift back
A sponge cake recipe calls for 2 teaspoons of baking powder, and the tin is empty. Use 1/2 teaspoon of baking soda and 1 teaspoon of cream of tartar, mixed into the flour before the wet ingredients go in. Cream of tartar is the dry acid that baking powder already contains, so this swap rebuilds baking powder from its own parts. Whisk the two into the flour thoroughly, add the wet ingredients, and get the tin into a fully preheated oven at once — the reaction starts the moment the liquid hits the soda.
Example 2: Sunday pancakes without a trip to the shop
A pancake recipe calls for 1 tablespoon of baking powder for a batch of twelve. Use 3/4 teaspoon of baking soda and 1 1/2 teaspoons of cream of tartar, whisked into the flour with the sugar and salt. The pancakes will rise and brown just as they should, because the cream of tartar gives the soda the acid it needs without adding any liquid or flavour. Cook them on a medium-hot pan and flip them when the bubbles on the surface stop filling in — that is the sign the lift has done its work.
Example 3: A batch of blueberry muffins
A muffin recipe calls for 1 teaspoon of baking powder per dozen. Use 1/4 teaspoon of baking soda and 1/2 teaspoon of cream of tartar, folded into the dry ingredients before the blueberries go in. Do not overmix once the wet and dry meet: stir just until the flour disappears, because every extra stir knocks gas out of the batter. Spoon the batter into the tin immediately and bake at once, and the muffins will dome nicely instead of spreading flat.
What changes in the result
The rise is the same when the ratio is right, because you are rebuilding baking powder from its own ingredients — soda plus acid. What can differ is the timing: this homemade version starts reacting as soon as it meets liquid, while commercial baking powder is double-acting and gives a second lift in the heat. In practice that means a batter made with this swap should go into the oven promptly, and the crumb may be a touch coarser. The flavour is unchanged when the ratio is exact, because the cream of tartar neutralises the soda completely and leaves no soapy aftertaste.
Flavour is the other thing to watch. Baking soda that has not fully reacted leaves a soapy, slightly metallic taste, and it can also yellow the crumb and darken the crust. That is the main reason the ratio is so small — a quarter of a teaspoon of soda does the work of a full teaspoon of baking powder, because baking powder is mostly filler and acid. If you double the soda 'to be safe', you will not get double the rise; you will get a bitter cake that spreads too much and then sinks. Trust the ratio, and if the bake comes out flat, the cause is usually stale soda or a slow oven, not too little leavening.
When not to substitute
Do not swap leavening in a recipe without acid — baking soda alone will taste soapy and will not rise. Do not use baking soda on its own in a recipe without acid — it will taste soapy and will not rise properly. And do not double the soda to get more lift: too much soda makes the crumb yellow, bitter and coarse, and it can make the cake sink after it rises.
There are also recipes where the swap is technically possible but not worth it. A delicate sponge, a chiffon cake or a recipe that depends on a very fine, even crumb will show the difference: the rise is a little less even and the crumb a little coarser. In those recipes, if you can wait, buy the right leavening. If you cannot wait, use the swap, expect a slightly rustic result, and serve it warm with something that flatters it — a custard, a compote, or a dusting of icing sugar covers a multitude of small imperfections.
Practical guidance
Test your baking soda before you trust it: drop half a teaspoon into a little vinegar or lemon juice. If it fizzes hard straight away, it is alive. If it barely bubbles, it is stale and no ratio will save the bake. Store baking soda and cream of tartar in airtight containers away from damp, and replace opened baking soda every few months — it absorbs smells from the fridge, which is useful there and ruinous in a cake. Mix the soda with the dry ingredients and the acid with the wet ingredients, then combine them at the last moment, so the reaction happens in the batter rather than in the bowl. And keep the oven door shut for the first two-thirds of the baking time: opening it early lets the heat out just as the crumb is setting, and a cake that has lost its lift will not recover.
Keep cream of tartar in a sealed jar away from damp; it keeps for years when dry. If you bake often, this is the most useful leavening swap to know, because cream of tartar is cheap, keeps well, and turns a tin of baking soda into baking powder whenever you need it.
Frequently asked questions
Is homemade baking powder as good as shop-bought?
For most everyday baking, yes. Shop-bought baking powder is baking soda plus an acid plus a little starch to keep it dry, and this swap rebuilds exactly that — soda plus cream of tartar. The one difference is timing: commercial powder is double-acting, so it gives a second lift in the oven heat, while the homemade version does most of its work as soon as it meets liquid. Get the batter into the oven quickly and the difference is hard to notice.
Can I mix a batch of homemade baking powder in advance?
You can, but use it within a few weeks and keep it bone dry: mix 1 part baking soda with 2 parts cream of tartar and 1 part cornflour, and store it in a sealed jar. Any damp will set the reaction off in the jar, and then it is useless. For a single bake, it is simpler to measure the two ingredients separately into the flour.
Can I use this substitute in every recipe that calls for baking powder?
In most everyday baking, yes — muffins, pancakes, quick breads, scones and simple cakes all take the swap well, as long as you follow the ratio of 1/4 tsp baking soda + 1/2 tsp cream of tartar per 1 tsp baking powder. Be more cautious with delicate sponges, chiffon cakes and anything where a very fine, even crumb is the whole point of the recipe. In those, the swap works but the texture is slightly coarser, so use it when you have no choice and accept a slightly more rustic result.
Why does my cake taste soapy after substituting?
A soapy or metallic taste almost always means too much baking soda, or soda that never met enough acid. Baking soda needs an acid to neutralise it; without one, the unreacted soda stays alkaline and tastes bitter and soapy. Check that you used 1/4 tsp baking soda + 1/2 tsp cream of tartar per 1 tsp baking powder and not a heaped spoon, and make sure the acid was actually in the batter. If the recipe has no acid at all, this swap is the wrong one — use the version that brings its own acid.
How do I know if my baking soda is still good?
Drop half a teaspoon into a tablespoon of vinegar or lemon juice. Fresh soda fizzes vigorously at once; stale soda barely bubbles. Baking soda goes flat over months, especially once the box is open, so test it before you bake with it. Cream of tartar keeps much longer, but keep it dry and sealed. If either one fails the test, replace it — a flat leavener is the most common reason a substituted bake does not rise.