Why brown sugar has to be "packed"
Brown sugar is granulated sugar coated in molasses, which makes the crystals clump and cling together rather than settling and pouring freely the way granulated sugar does. Scooped loosely, a cup of brown sugar traps a lot of air and its weight becomes unpredictable — anywhere from 145g to 200g depending on how it was handled. Pressing it firmly into the cup with the back of a spoon squeezes that air out and gives a repeatable measurement: about 220g per packed cup. That's why virtually every recipe that calls for brown sugar says "packed" explicitly, and why you should assume packed even when a recipe just says "1 cup brown sugar" without the word.
A properly packed cup should hold the shape of the measuring cup for a moment when turned out onto a surface. If it collapses immediately, it wasn't packed firmly enough.
Light vs. dark brown sugar — does the weight change?
Barely. Light brown sugar is roughly 3.5% molasses by weight; dark brown sugar is roughly 6–7%. That's enough to noticeably change color, flavor (dark has a stronger, more caramel-like taste), and moisture, but not enough to meaningfully change the weight of a packed cup — both land close enough to 220g that recipes treat them as interchangeable by weight. Use dark where you want a deeper molasses flavor (gingerbread, BBQ sauce, dark caramel) and light where a milder sweetness is preferred (most cookies, cakes).
No brown sugar? Make your own
Brown sugar is just granulated sugar plus molasses, so you can reconstruct it in under a minute: for every 1 cup of packed brown sugar a recipe calls for, mix 1 cup granulated sugar with 1 tablespoon molasses for a light-brown equivalent, or 2 tablespoons molasses for dark. Stir (a fork or the paddle attachment on a stand mixer works well) until the molasses is evenly distributed and the mixture looks uniformly brown with no wet streaks, then pack it into your measuring cup as normal.
| Brown sugar needed | Granulated sugar | Molasses (light) | Molasses (dark) |
|---|---|---|---|
| ½ cup | ½ cup | 1½ tsp | 3 tsp |
| 1 cup | 1 cup | 1 Tbsp | 2 Tbsp |
| 2 cups | 2 cups | 2 Tbsp | 4 Tbsp |
Quick reference chart
| Cups (packed) | Grams |
|---|---|
| ¼ cup | 55g |
| ⅓ cup | 73g |
| ½ cup | 110g |
| ⅔ cup | 147g |
| ¾ cup | 165g |
| 1 cup | 220g |
| 2 cups | 440g |
FAQ
Can I use light and dark brown sugar interchangeably? Yes, in most recipes — the weight and sweetness are nearly identical, so swapping mainly changes color and the strength of the molasses flavor, not how the recipe bakes.
My brown sugar turned into a hard block — is it ruined? No — it's just lost moisture. Microwave it briefly next to a cup of water, or seal it in a bag with a slice of bread or a damp paper towel overnight, and it will soften back to packable consistency.