Corn syrup

One US cup of corn syrup weighs 320 grams. Going the other way, 100 grams is about 0.31 cups.

Corn syrup is a concentrated glucose solution made by breaking down corn starch enzymatically until the starch molecules become simple sugars. It is one of the densest liquid ingredients in a home kitchen, sitting in the same range as honey, molasses and maple syrup — all concentrated sugar solutions with similar water content and similar density around 1.3 to 1.4 grams per millilitre.

USDA FoodData Central publishes 1 cup at 320 grams and 1 tablespoon at 20 grams (FDC 168836, Syrups, corn, light). This gives a bulk density of 1.3527 grams per millilitre. King Arthur's ingredient weight chart publishes 1 cup at 312 grams and 1.3187 grams per millilitre. The two figures agree within 2.5 percent, comfortably inside the 5 percent tolerance we apply to the syrup category.

We publish the USDA figure of 320 grams per cup because it comes with the underlying tablespoon and 100-gram numbers rather than an extrapolation from a partial cup, and because USDA's laboratory measurements are more rigorous than a chart entry.

Corn syrup should not be confused with high-fructose corn syrup, though the density is nearly identical. Regular corn syrup (the kind sold in bottles under the Karo brand) is predominantly glucose. High-fructose corn syrup is regular corn syrup that has been further processed with an enzyme to convert some of the glucose to fructose, producing HFCS-42 (42 percent fructose) or HFCS-55 (55 percent fructose). HFCS is used almost exclusively in commercial food manufacturing rather than home baking; the bottle on the supermarket shelf is regular glucose corn syrup. Both have density near 1.35 grams per millilitre because the total sugar content is similar; the distinction is in the sugar type and sweetness, not the weight per cup.

Light and dark corn syrup differ only slightly. Dark corn syrup is light corn syrup with molasses or refiners' syrup added for colour and a slight caramel note; the density is essentially the same at 320 to 325 grams per cup. King Arthur does not publish a separate row for dark, and USDA lists them separately with only a few grams of difference. For measurement purposes, treat them as interchangeable and rely on the recipe's flavour requirement to choose between them.

Related concentrated sugar syrups: honey (339 g/cup, density 1.43), molasses (337 g/cup, 1.42), maple syrup (322 g/cup, 1.36), sweetened condensed milk (306 g/cup, 1.29). All sit in the same density range because all are concentrated aqueous solutions of sugars, and all measure similarly in a cup — thick, slow to pour, self-levelling once settled, insensitive to how the cup is filled.

A cup of corn syrup weighs about 2.4 times more than a cup of water, which is why recipes that call for it as part of the liquid balance need to weigh rather than measure by volume when the ratio matters — pecan pie and caramel are the two clearest examples, where 10 percent too much or too little corn syrup changes the final texture from set to runny or set to hard.

FDA does not publish an identity standard for corn syrup as a common name; it is regulated under general food safety and labelling rules. The Codex Alimentarius standard for sugars (CXS 212-1999) covers glucose syrups and related sweeteners internationally, addressing composition and identity rather than density.

The category here is 'syrup' rather than 'liquid' because corn syrup's measuring behaviour matches other concentrated sugar solutions: thick, slow-pouring, and not sensitive to how the cup is filled once it settles. The 5 percent syrup tolerance applies, and both sources sit well inside it.