Volume

The unit opens by counting how many 1 cm³ blocks fill a solid, then moves to the length times width times height formula and on to capacity measured from the inside of a container. Conversions between volume units, the link between the volume of water and its weight, and composite solids such as L-shapes, staircases and shapes with a hole through the center all follow.

With capacity, the standard error is working from the outside dimensions without subtracting the thickness, so the answer comes out too large. In conversions, 1 L = 1000 cm³ and 1 m³ = 1000000 cm³ get mixed, leaving the answer off by three zeros. With composite solids, the missing part sometimes gets subtracted twice.

Not surface but a new quantity, volume, is what gets measured from here on. Telling faces and vertices apart was already confirmed in Rectangular Prisms and Cubes in grade 4. The method fixed here, base area times height, generalizes in grade 6, when Volume of Prisms and Cylinders extends it to shapes beyond the box.