How to convert baking soda
Our reference is 288 grams per US reference cup of baking soda, levelled measure of bicarbonate of soda. That works out to about 1.2173 grams per millilitre, so cups = grams ÷ 288 and grams = cups × 288 in US customary measures.
For metric and Australian recipes the cup holds 250 ml, so one cup of baking soda is about 304.33 grams. Australian tablespoons hold 20 ml rather than 15 ml, which the calculator handles when you pick that system.
Preparation changes the weight
The reference describes baking soda as: levelled measure of bicarbonate of soda. A different form, such as sifted, packed, melted, chopped or cooked, can hold a different weight in the same cup and needs its own reference. When a recipe gives a gram amount, weigh that amount instead of converting.
Brand, moisture and how firmly the cup is filled all move the practical result. Treat the numbers here as recipe equivalents, not laboratory densities.
Where the number comes from
The reference comes from King Arthur Baking ingredient weight chart, which lists 1/2 teaspoon as 3 grams. Published weight of 3 g per half teaspoon, multiplied by 96 half-teaspoons per US cup. Cup quantities of a leavener are not a recipe amount; the reference exists to keep teaspoon and gram conversions consistent. This site assigns the published cup weight to its adopted US reference cup of 236.5882365 ml; the source itself does not define an exact millilitre cup volume. Checked September 26, 2026.