Start with a cube as shown below and call the length of one side a:

The area of one square is a × a = a

Since there are six sides, the total surface area, call it SA is:

SA = a

SA = 6 × a

Find the surface area if the length of one side is 3 cm

Surface area = 6 × a

Surface area = 6 × 3

Surface area = 6 × 3 × 3

Surface area = 54 cm

Find the surface area if the length of one side is 5 cm

Surface area = 6 × a

Surface area = 6 × 5

Surface area = 6 × 5 × 5

Surface area = 150 cm

Find the surface area if the length of one side is 1/2 cm

Surface area = 6 × a

Surface area = 6 × (1/2)

Surface area = 6 × 1/2 × 1/2

Surface area = 6 × 1/4

Surface area = 6/4 cm

Surface area = 3/2 cm

Surface area = 1.5 cm