Definition
Unit cube
A unit cube has edges 1 unit long and a volume of 1 cubic unit.
What it means
A unit cube is the 3-D “one” used for volume. Pack identical cubes through the whole solid—across, back, and up. The number of cubes, including any hidden inside or behind, is the volume in cubic units.
Remember it
Volume counts cubes through all three directions, not just the cubes you can see.
Example
A box is 4 unit cubes long, 3 cubes deep, and 2 cubes high. Each layer has 4 × 3 = 12 cubes, and there are 2 layers, so the box contains 24 unit cubes and has volume 24 cubic units.
Watch for
A cube with edges 2 units long is not one unit cube; it contains 2 × 2 × 2 = 8 unit cubes and has volume 8 cubic units.
Common mix-up
A unit cube measures volume in cubic units. A unit square measures area in square units.
Exact meaning
A unit cube is a cube whose three edge dimensions are 1 unit by 1 unit by 1 unit, so its volume is 1 cubic unit. Copies of the same unit cube can measure a solid’s volume when they pack it completely without gaps or overlaps.