100 grams of rolled oats is 3.53 oz (100 g) by weight. It is about the size of a coffee mug and occupies 1.06 cups (250 mL) of volume.

In kitchen measures
1.06 cups
50.7 tsp · 16.9 tbsp · 1.06 cups
about the size of a coffee mug
Rolled oats typically ranges 0.38–0.48 g/mL depending on how it's packed. A firmly packed scoop weighs more.