0.25 cups of walnuts is a common serving size for baking or snacking. It is about the size of a large egg when poured into a loose pile.

In kitchen measures
4 tablespoons
12 tsp · 4 tbsp · 0.25 cups
about the size of a large egg
Density estimated by AI from typical values. Walnuts typically ranges 0.38–0.52 g/mL depending on how it's packed. A firmly packed scoop weighs more.