How many grams is 1 tablespoon of light brown sugar?

1 tablespoon of light brown sugar (brown sugar) weighs

14g

That's 0.5oz. An Australian 20ml tablespoon holds 19g.

A level US or UK tablespoon (15ml). USDA doesn't measure a tablespoon of this, so this is a sixteenth of its cup weight.

American recipes mean firmly packed unless they say otherwise. A loosely filled cup weighs about a third less.

Other amounts of light brown sugar

Where these numbers come from

USDA FoodData Central, SR Legacy, food 19334: “Sugars, brown”. USDA lists these household measures for it:

1 tsp unpacked = 3g
1 cup packed = 220g
1 cup unpacked = 145g
1 tsp packed = 4.6g
1 tsp brownulated = 3.2g

Fractions of a cup are the cup weight scaled down. The tablespoon figure is the cup weight divided by 16, since USDA doesn't list a tablespoon for this ingredient. Metric-cup figures assume a 250ml cup, and Australian tablespoons hold 20ml. Weights under 10g are rounded to 0.1g, everything else to the nearest gram. Full source list.