Check the net weight first
Recipes sometimes say ‘one box’ because an older package size was familiar to the writer. Current products can be sold in several sizes, so the word box cannot safely be converted into one universal number.
Read the package net weight in ounces or grams. Then use a source-matched conversion or weigh the amount the recipe needs.
Manufacturer equivalents
Domino and C&H each publish approximately 2⅓ firmly packed cups per 1 lb, 4⅔ cups per 2 lb, and 10 cups per 4 lb. Keep the word approximately and the firmly-packed condition; do not turn those tables into an unsupported exact gram figure.
C&H's method is to scoop sugar into the cup, press until compact, repeat until full, and level flush with the rim.
Box weight is not the same as cup weight
A package label gives mass. A cup is volume. Brown sugar's moisture and packing affect how much space a given mass occupies, so use the package label and the recipe's measurement method together.
Questions readers ask
Does one box of brown sugar always equal 1 pound?
No. Current product pages show several package sizes, so check the net-weight label instead of assuming a box is 1 lb.
How many cups are in a 2 lb box?
Domino and C&H list approximately 4⅔ firmly packed cups for a 2 lb package.
Should brown sugar be packed?
Use the recipe's instruction. The manufacturer equivalents on this page are for firmly packed brown sugar, not loose sugar.
Can I calculate grams from a box?
Yes, when you know the package net weight, but keep the package mass separate from any cup estimate and do not attribute a derived number to the manufacturer.
Sources and method
Numerical answers are tied to the stated ingredient, state, cup convention, and source. Derived values are calculated from the cited reference and rounded for kitchen use.