Free Sugar Weight to Volume calculator with clear step-by-step results.
Sugars differ by a factor of two per cup - icing sugar is aerated at about 120 grams while packed dark brown reaches 240 - so treating them interchangeably by volume causes large errors. Brown sugars are quoted packed, as recipes assume.
Cups
Cups = grams / grams per cup for that sugar
Spoon equivalents
1 cup = 16 tablespoons = 48 teaspoons
Yes - recipes assume firmly packed brown sugar. Loosely spooned, a cup holds about 25% less and the bake will be drier and less chewy.
It is milled to a fine powder with anti-caking starch and traps a great deal of air. It should also be sifted, which reduces the packed weight further.