Volume of a Rectangular Prism Year 6 Mathematics · 3D Space & Structures · WA6MMGTH1–TH2 One layer = 4 x 3 = 12 cubes2 layers high -> 12 x 2 = 24 cubic units The base layer fills first, then a second identical layer stacks on top: 12 × 2 = 24 cubic units.