Baking soda

One US cup of baking soda weighs between 220.8 and 288 grams, depending on how the cup is filled and which source measured it. That range is the answer; a single number would not be. Every figure behind it is below, with the method each source used.

Baking soda is unusual on this site in that almost nobody measures it by the cup. The typical recipe calls for half a teaspoon or one teaspoon at a time, and the small amount means small errors do not matter much for the final product. Both of our sources publish figures for the teaspoon rather than the cup, and the cup figure below is extrapolated from the teaspoon.

USDA FoodData Central publishes 1 teaspoon = 4.6 grams (FDC 175040, Leavening agents, baking soda), which extrapolates to 220.8 grams per cup and a bulk density of 0.9333 grams per millilitre.

King Arthur's chart publishes 1/2 teaspoon = 3 grams, which extrapolates to 6 grams per teaspoon, 288 grams per cup, and a bulk density of 1.2174 grams per millilitre. King Arthur publishes only to the whole gram, so 3 grams rounded implies a real value between 2.5 and 3.5 grams per half teaspoon.

The two figures are both physically plausible. Baking soda's bulk density varies with how tightly it is packed: loose or aerated is around 0.7 g/mL, a regular pour is around 0.9-1.0 g/mL, and tapped or compacted approaches 1.2 g/mL. Sodium bicarbonate's crystalline density is 2.20 g/mL, so anything up to that is theoretically possible with enough compaction. Our two sources appear to have measured under different conditions — USDA at a regular pour, King Arthur at something closer to a tapped or scooped measurement.

Because neither source names its method and the spread is 30 percent, we publish the range rather than a single figure. The teaspoon range is 4.6 to 6.0 grams; the cup range is 221 to 288 grams.

Baking soda is sodium bicarbonate (NaHCO3), and should not be confused with two neighbouring products. Baking powder is a mixture that contains sodium bicarbonate plus an acid and often a starch buffer, and weighs differently per cup because of the added components. Washing soda (sodium carbonate, Na2CO3) is a related substance used for cleaning and food processing, not for baking. Neither is interchangeable with baking soda in a recipe.

Neither the United States Pharmacopeia nor the Food Chemicals Codex publishes bulk density for sodium bicarbonate; both address purity and particle-size specifications rather than volume measurement.

For a home baker, the practical implication of the source disagreement is small. Recipes calling for baking soda in teaspoons are already tolerant to a factor-of-two error before the leavening turns visibly wrong. The disagreement matters only when a recipe specifies baking soda by the cup or by weight, in which case knowing which source the recipe used becomes essential.

The category here is 'milled' rather than 'sugar' or 'salt' because baking soda's measurement behaviour — a fine powder that clumps and bridges — matches the milled category we already use for cocoa powder, cornstarch, and almond flour.