Definition
Surface area
Surface area is the total area covering the outside of a three-dimensional object.
What it means
Surface area asks how much covering would wrap the whole outside. A box has several faces, so find the area of each face and add them. Curved outer surfaces count too, even when they do not unfold into rectangles.
Remember it
Imagine unfolding the outside into flat pieces, then adding the area of every piece.
Example
A rectangular box is 4 cm long, 3 cm wide, and 2 cm high. Its paired faces have areas 12, 8, and 6 cm², so its surface area is 2 × (12 + 8 + 6) = 52 cm².
Watch for
Surface area measures the outside covering, not the space the object occupies inside.
Common mix-up
Volume uses cubic units for inside space; surface area uses square units for the outside.
Exact meaning
The surface area of a three-dimensional object is the sum of the areas of all its outer surfaces, measured in square units. For a flat-faced solid, it is the total area of every face.