Onion Powder

One US cup of onion powder weighs 110.4 grams. Going the other way, 100 grams is about 0.91 cups.

Also called onion powder, powdered onion, dried onion powder, dehydrated onion powder, ground onion.

A US cup of onion powder weighs 110 grams, a figure on which USDA's reference weight and an independent foodservice measurement agree within 4%, comfortably inside the 10% tolerance held for spices.

Onion powder is dehydrated onion milled to a fine powder. The spice trade also sells granulated onion, a coarser grind, and minced or chopped dried onion, coarser still. Onion salt is a different product altogether: onion powder blended with salt, which makes it far heavier per spoon and far saltier, and it should never be measured as a substitute. This entry covers the product sold as onion powder.

USDA's SR Legacy record lists 6.9 grams per tablespoon and 2.4 grams per teaspoon, which scale to 110.4 and 115.2 grams per cup. A foodservice conversion table built from measurements across several vendors lists onion powder at 3.75 ounces per cup, or 106.3 grams, and the same page's rule of thumb of 0.45 teaspoons per gram works out to 107 grams, so that source agrees with itself. The published figure uses USDA's tablespoon basis. The teaspoon basis runs 4% higher only because a 2.4 gram portion is rounded more coarsely than a 6.9 gram one.

The physics is worth a closer look, because onion powder is much lighter than its closest relative. Like garlic powder, it is almost fat-free, at about 1% fat, 79% carbohydrate, and 10% protein by USDA composition, so neither powder has the oily, tacky particle film that governs paprika. Yet garlic powder runs 127 to 155 grams per cup, well above onion powder's 110. The likely reason is the starting tissue. Fresh onion is close to 90% water, while fresh garlic is under 60%. Drying a much wetter tissue leaves a more porous solid, so each onion powder particle carries more internal void and the cup weighs less. The two onion powder sources also show none of the grind split that separates the garlic powder data, which is why this entry can publish a single figure.

Onion powder is strongly moisture-sensitive and cakes quickly once a jar is opened in a humid kitchen. Caked lumps pack heavier than loose powder, so a hardened jar will overshoot this figure when scooped. Break lumps up before measuring, or replace the jar if it has set solid.

In practice, a teaspoon of onion powder weighs 2.3 grams and a tablespoon 6.9 grams. For everyday seasoning, measure by spoon. For dry rubs and seasoning blends made in quantity, weigh it. When swapping between onion powder and granulated onion, go by weight rather than volume, since the coarser grind packs differently and no reliable cup weight for granulated onion has been published. Spoon it into the measure and level without pressing, and keep the jar tightly closed.