You would be more likely to find the mass of a pen in grams rather than kilograms because the weight of a pen is not as high as 1 kilogram and it is closer to an amount of grams.
A gram (g) is used to measure the weight or mass of very light objects. A small paperclip weighs about a gram. A kilogram (kg) is used to measure the weight or mass of heavier objects. A one-liter bottle of water weighs about a kilogram.
