The 14 + 2 Cake Flour Rule
Cake flour is milled from soft wheat to a low protein content, around 7 to 9 percent, which means it forms less gluten and bakes into the fine, cottony crumb you want in a layer cake, chiffon, or sponge. All-purpose flour runs 10 to 12 percent protein, so on its own it can leave a cake denser and chewier. The classic bakers fix is to swap in a little cornstarch, which is pure starch with zero protein, to dilute the flour back down toward cake-flour territory. The rule is simple: for every 1 cup of cake flour, measure 1 cup of all-purpose flour, remove 2 tablespoons, and add 2 tablespoons of cornstarch in their place. That leaves you with 14 tablespoons of all-purpose flour plus 2 tablespoons of cornstarch per cup.
Why You Have to Sift
The swap only works if the cornstarch is evenly spread through the flour. Sifting the two together two or three times disperses the starch and aerates the blend, which is exactly what makes commercial cake flour so light. Skip the sifting and you can end up with chalky pockets of starch in the baked crumb.
per cup cake flour = (1 cup AP flour - 2 tbsp) + 2 tbsp cornstarch = 14 tbsp AP + 2 tbsp cornstarch
Measuring by Weight Is More Reliable
A cup of flour can vary by 20 grams or more depending on whether you scoop or spoon it. If you have a kitchen scale, this calculator gives the blend in grams: about 105 grams of all-purpose flour plus 16 grams of cornstarch per cup of cake flour, totaling roughly 120 grams, the standard weight of a cup of cake flour. Weighing removes the guesswork and is the single best upgrade for consistent cakes.
Frequently Asked Questions
What is the exact ratio of all-purpose flour to cornstarch for cake flour?
For every 1 cup of cake flour, use 14 tablespoons of all-purpose flour plus 2 tablespoons of cornstarch, which equals one level cup of all-purpose flour with 2 tablespoons removed and replaced by cornstarch. Always sift the two together two or three times so the cornstarch is evenly distributed and the blend is light.
Can I use cornstarch substitutes like arrowroot or potato starch?
Yes, arrowroot powder and potato starch both work as one-to-one stand-ins for cornstarch in this swap because they are also protein-free starches that soften the crumb. This calculator lets you pick your starch and adjusts the gram weight slightly, since potato starch is a touch heavier per tablespoon. The volume measurement stays the same at 2 tablespoons of starch per cup.
Will a homemade cake flour substitute work as well as the real thing?
For most cakes the difference is negligible once you sift well, and many bakers cannot tell the two apart in a finished layer cake or cupcake. The one place store-bought cake flour has a slight edge is in very delicate angel food and chiffon cakes, where the finer, more uniform milling can give a hair more lift. For everyday baking the 14-plus-2 swap is a trusted, reliable fix.
How do I measure the flour so the substitute is accurate?
Spoon the flour into your measuring cup and level it off with a straight edge rather than scooping the cup directly into the bag, which packs in extra flour and can add 20 grams or more per cup. Better still, weigh it: a cup of the finished cake-flour blend should weigh about 120 grams. Accurate measuring matters more than the brand of flour you start with.
Practical Guide for Cake Flour Substitute Calculator
The reason this swap works comes down to gluten. When you add water and mix, the proteins in flour link up into gluten, the stretchy network that gives bread its chew. Cakes want the opposite: just enough structure to hold their shape and not a gram more. Replacing 2 tablespoons of all-purpose flour with 2 tablespoons of cornstarch per cup lowers the overall protein percentage of your blend, so less gluten forms and the crumb stays soft and fine. It is the same principle behind why some bakers also reach for a lower-protein brand of all-purpose flour as their starting point.
Sifting is not optional with this method, and it is worth understanding why. Cornstarch is a very fine, dense powder that wants to clump and settle to the bottom of the bowl. If it is not fully blended, parts of your batter get a double dose of starch while others get almost none, which shows up as a slightly gummy or chalky texture in the baked cake. Running the all-purpose flour and starch through a sieve together two or three times breaks up clumps, mixes them uniformly, and aerates the blend so it folds into wet ingredients more smoothly. Think of the sifting as the step that actually creates the cake flour.
Where you can be flexible is the starch itself. Cornstarch is the default, but arrowroot powder and potato starch are both protein-free and behave almost identically in this role, so use whichever is in your pantry at the same 2-tablespoons-per-cup ratio. What you should not substitute is self-rising flour or bread flour for the all-purpose base, since self-rising already contains leavening and salt that will throw off your recipe, and bread flour has even more protein than all-purpose, pushing the crumb in exactly the wrong direction. Start with plain all-purpose flour every time.
Quick Checklist
- Per cup of cake flour: 14 tbsp all-purpose flour + 2 tbsp cornstarch.
- Sift the flour and starch together two to three times before using.
- Spoon and level your flour, or weigh it at about 120 g per cup.
- Swap in arrowroot or potato starch one-to-one if you are out of cornstarch.