Cream of tartar

One US cup of cream of tartar weighs between 144 and 162 grams (5.1 to 5.7 ounces), 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.

Cream of tartar weighs 144-162 g/cup depending on source. USDA's food composition reference sits at the low end (3 g/teaspoon = 144 g/cup); McCormick's brand label lands in the middle (0.8 g per 1/4 teaspoon = 154 g/cup); professional culinary references and baking aggregators cluster at the high end (3.4 g/teaspoon = 162 g/cup).

Cream of tartar is potassium bitartrate, a fine crystalline powder that is a natural byproduct of winemaking. Tartaric acid crystallizes on the inside of wine barrels during fermentation; those crystals are collected, purified, and milled to produce the ingredient sold in the spice aisle. Chemically it is a mild acid salt with the formula KC4H5O6, sold under the European food additive code E336. In baking, it serves three main functions: stabilizing beaten egg whites for meringues and angel food cake, activating baking soda when baking powder is not available, and preventing sugar syrup from crystallizing in candy and caramel work.

King Arthur has no cream of tartar entry on their Ingredient Weight Chart, so this catalog entry is based entirely on producer labels and reference sources.

The density spread across sources reflects real physical variance rather than disagreement about what cream of tartar is. The powder is finely crystalline and packs differently depending on how much it has settled during shipping and storage, and it absorbs a small amount of ambient humidity that shifts its bulk density. Fresh from an unopened jar, cream of tartar typically packs closer to the 154-162 g/cup end of the range; after months of pantry storage in a household humidity cycle, it can compress toward the 144-150 g/cup end. Neither is 'correct' — both reflect the ingredient at different points in its handling life.

USDA's 3 g/teaspoon figure is worth understanding as a nutrition-database convention rather than a precision density measurement. USDA FNDDS and SR Legacy entries for leaveners typically round to convenient whole-gram values because the primary purpose of the database is calorie and macronutrient calculation, where small variations in leavener weight are nutritionally negligible. McCormick's 0.8 g per quarter-teaspoon figure, by contrast, is unusually precise for a supplement-style label, and their inclusion of the 0.8 rather than a rounded 1.0 suggests genuine measurement. The professional culinary reference at 0.68 g/cm³ bulk density (giving 162 g/cup) represents laboratory-condition measurements of newly-opened product.

Practical baker guidance: cream of tartar is almost always used in tiny per-recipe volumes — 1/4 teaspoon per egg white for stable meringue, 1/2 teaspoon for a batch of snickerdoodles, 1 to 2 teaspoons in DIY baking powder combinations. At these amounts, the density variance across the range represents fractions of a gram and does not affect recipe outcomes. Weight-based measurement matters only for larger applications such as commercial candy production or bulk baking powder manufacture.

Common substitutions: for egg white stabilization, lemon juice or white vinegar at roughly 1/8 teaspoon per egg white can substitute for 1/8 teaspoon of cream of tartar, though the added liquid may slightly alter texture. For baking soda activation, cream of tartar is difficult to replicate — the acid substitution options are more application-specific (buttermilk, yogurt, molasses, or brown sugar can each provide the acid needed depending on the recipe). For DIY baking powder, the classic ratio is 1/2 teaspoon cream of tartar plus 1/4 teaspoon baking soda plus 1/4 teaspoon cornstarch to make 1 teaspoon of single-acting baking powder.