The gram (g) is the metric unit used for small masses, such as food and letters. The kilogram is the SI base unit of mass, so a gram is 1/1,000 kg under the International System of Units. A gram is about 0.03527 ounces.
Conversion
g = kg × 1000
g = oz × 28.34952
oz = g ÷ 28.34952
g = lb × 453.5924
Example
A 250 g pack is 250 ÷ 28.34952 = 8.82 oz and 250 ÷ 453.5924 = 0.551 lb. A 2.5 kg bag is 2.5 × 1000 = 2,500 g.
The guide to grams in an ounce has full charts; cups to grams shows why volume needs a density. The converters grams to ounces and grams to kg cover other values.
Common mistakes
A gram measures mass, so converting grams to cups or fluid ounces needs the density of the ingredient. Water is close to 1 g per mL, but flour, oil and honey are not. Treating the ounce as 30 g also overstates it by 5.8% (30 ÷ 28.34952 = 1.058), which adds up across a large recipe.