Crisp rice cereal

One US cup of crisp rice cereal weighs 28.3 grams (1.00 ounces). Going the other way, 100 grams is about 3.53 cups.

Crumbs and cereals compared: cup weights side by side, the source behind each, and why they differ.

A cup of crisp rice cereal weighs about 28.3 g (1 oz). America's Test Kitchen weighed ten cups at 283 g, King Arthur Baking's chart says 28 g, and USDA and Kellogg's labels put it at 26.4 to 26.7 g, all within 7.2%.

Crisp rice cereal is rice that is cooked, dried and toasted until each grain puffs into a light, hollow, crackling shell; Kellogg's sells it as Rice Krispies and store brands as crisp or crispy rice. Its biggest job in the kitchen is the marshmallow treat, but it also goes into no-bake bars and clusters, chocolate bark, ice cream pie crusts, and coatings for chicken and fried ice cream.

America's Test Kitchen's crispy rice cereal treats use 10 cups of cereal and give the weight as 10 oz, 283 g, 28.3 g a cup. Weighing ten cups at once averages out the small differences between one cupful and the next, which makes it the most precise figure here, so this site publishes it. King Arthur Baking's chart gives 1 cup of Rice Krispies as 1 oz, 28 g, 1% lighter, and this page accepts it. USDA's record for Rice Krispies gives the cereal's serving of 1 1/4 cups as 33 g, 26.4 g a cup, and Kellogg's current label gives 1 1/2 cups as 40 g, 26.7 g a cup. All four are within 7.2%, inside the 10% this site allows for cereals and other milled ingredients, and confidence is high.

The slightly lighter label figures fit a serving line rather than a weighed cup: cereal labels start from a reference weight of about 40 g and round the cup to the nearest quarter, and 1 1/2 cups is the nearest quarter cup to 40 g. Test Kitchen and King Arthur both weighed cereal in a measuring cup.

The physical check: each puffed grain is a thin shell around air, and the shells themselves are light, so crisp rice is one of the lightest ingredients on this site, about an eighth of a gram per millilitre. Corn flakes weigh about the same per cup, 28 g, and uncooked rice several times as much, because puffing turns each grain into a hollow shell many times its original size. Puffed grains are round and roll into gaps, so they fill a cup more evenly than flakes do.

Practical guidance: use 28 g per cup of crisp rice cereal, about 1.8 g per tablespoon. The classic recipe for marshmallow treats takes 6 cups, about 170 g; Test Kitchen's takes 10 cups, 283 g. A 12 oz box holds about 12 cups and an 18 oz box about 18. For treats, weigh the cereal and the marshmallows if you can, so the ratio stays the same from batch to batch.