1/2 cup of brown sugar (packed) to grams

Brown sugar refuses to behave like a normal dry ingredient because it isn't really dry. Each crystal is coated in a thin film of molasses, and that sticky molasses layer is what makes the sugar cohesive, compressible, and wildly variable by volume. Press it into a cup and the molasses film acts as a binder, locking crystals together so a one-cup measure can hold anywhere from 180 to 240 grams depending on how hard you pack it. Leave it loose and the same cup might hold 145 grams of fluffy, air-pocketed sugar. The crystals themselves are similar in size to granulated white sugar, but the surface coating changes everything: it absorbs and releases moisture from the air, hardens into clumps when exposed to dry kitchens, and softens back when sealed with a piece of bread or a damp paper towel. Dark brown sugar carries more molasses than light brown sugar (roughly 6.5 percent versus 3.5 percent by weight), which is why dark brown packs slightly denser and tastes more assertive, but for measurement purposes the King Arthur Baking ingredient weight chart treats both at 213 grams per packed US cup, and that single packed standard is what every reliable recipe assumes.

The mistake almost every home cook makes is treating "1 cup brown sugar" the way they treat "1 cup flour," scooping it loosely and leveling the top with a knife. That gives you something closer to 145 grams instead of 213, and you've now under-sugared the recipe by roughly a third. Cookies spread less, brown less, and lose the chewy edge that the molasses moisture creates. Recipes default to packed brown sugar unless they explicitly say "loosely measured," because the packed measurement is the only one that produces a repeatable weight in a household kitchen.

To pack it correctly, spoon brown sugar into a dry measuring cup until it mounds slightly above the rim, then press it down firmly with the back of a spoon or your knuckles, working from the edges to the center. Add a little more if needed and press again. You're done when the surface holds the shape of the cup after you tip it out, the way wet sand holds the shape of a beach pail. If a quarter cup of sugar tips out as a clean little dome, you packed it right. A kitchen scale eliminates the guesswork entirely: 213 grams per cup, 53 grams per quarter cup, 13 grams per tablespoon, full stop.

Density matters most in cookies, where brown sugar is doing structural and textural work, not just adding sweetness. The molasses contributes acid that activates baking soda, moisture that keeps the interior chewy, and hygroscopic compounds that pull water from the air during cooling. Under-measure and your chocolate chip cookies turn out pale, crisp, and short-lived. Over-measure and they spread into thin puddles. Caramel sauces and butterscotch are equally sensitive: the ratio of brown sugar to butter and cream determines whether the sauce sets to a soft pour or a stiff candy. Brown sugar glazes for ham, barbecue rubs, and pecan pie filling all rely on the molasses-to-crystal ratio for both flavor and viscosity. Quick breads and muffins are more forgiving, but anything where you want a chewy crumb (banana bread, blondies, oatmeal cookies) lives or dies by getting the brown sugar weight right.

For substitution, light and dark brown sugar are interchangeable by weight in nearly every recipe; the only difference you'll taste is a deeper, more bitter molasses note in the dark version, which suits gingerbread, barbecue sauce, and dark chocolate desserts. If you're out of brown sugar, mix one tablespoon of unsulphured molasses into one cup (200 grams) of granulated white sugar for a light brown substitute, or two tablespoons for dark brown; rub it in with your fingertips until uniformly colored. Muscovado is an excellent upgrade rather than a substitute, denser and moister than standard brown sugar, so reduce the volume by about 10 percent or measure by weight. Coconut sugar has a similar color but lacks the molasses moisture, so it changes both texture and flavor; treat it as a different ingredient, not a swap.