Volume is how much space something takes up. Fill a box with cubes, one layer at a time.
Count every cube, even the ones hiding at the back.
Volume is how many cubes fit inside.
Count one layer, then times by how many layers.
Volume = length × width × height, in cm3.
Missing side? Divide the volume by one layer.
Volume is how much space a solid shape takes up. We measure it by counting how many cubes would fit inside it. With centimetre cubes, the volume is in cubic centimetres, written cm³.
Multiply the length by the width to find how many cubes fit in one layer, then multiply by the height, which is how many layers there are. A box 4 cm long, 3 cm wide and 2 cm high holds 4 × 3 × 2 = 24 cm³.
In a picture of a box, the cubes at the back and in the middle are hidden. Counting a layer at a time, then the number of layers, makes sure none are missed.
Children build shapes from cubes and count them at about 9 to 10, and work out the volume of a cuboid with length × width × height in cm³ at about 10 to 11.