Mensuration for a Cube of length of side 20 units: Volume, Surface Area, Diagonal and Circumradius

You are given a cube of length of side 20 units. 

Computing the Total Surface Area, Volume and Diagonal of the cube

Side (or length) of the cube = 20 units. 
Total Surface area of the cube = 4 * side2 = 4 * 20 * 20 = 1600 square units.
Volume of the cube = side3 = 20 * 20 * 20 = 8000 cubic units. 
Length of the diagonal of the cube = (3 * side2)0.5 = 34.64 units  (Extending the Pythagorean theorem to three dimensions)

You might also make these calculations by considering the cube to be a special case of other 3D hexahedrons: an equilateral cuboid or a regular square prism or a square parallelopiped. 

Circumsphere of the Cube

A sphere touching all six vertices of a cube is known as its circumsphere. 
The circumsphere of this cube as a radius equal to (length of the diagonal)/2 = 17.32

Now, if we know that the cube is made of Iron and we measure the side in centimetres and the density of the material is 2.7 grams per cubic centimetre, we can calculate the mass of the cube:
Mass of the cube = Density x Volume = 21600.0 grams. 

All cubes are geometrically similar. 

Let's compare this current cube (let's call it cube A) with a cube B of side 10 units
The scale factor A : B = 20:10
Ratio of surface areas of A : B  = 1600: 400 = 4 : 1 (this holds true whether you compare total surface area or surface area per side, or any corresponding pairs of surface areas between the cubes)
Ratio of volumes of A:B = 8000 : 1000 = 8 : 1

While working with scale factors, square the scale factor to determine the area of the new figure. Area involves two dimensions multiplied together. With scale factor, all you're really doing is multiplying the scale factor times itself.
Similarly the ratio of volumes will be the cube of the scale factor - as you're multiplying the scale factor thrice.

You may find some more useful notes and information about the cube over here.

Some more example(s):

Geometric Properties of a cube of size 21 units: Properties like Surface Area, Volume, Circumradius, Circumsphere, Mensuration etc.

Geometric Properties of a cube of size 22 units: Properties like Surface Area, Volume, Circumradius, Circumsphere, Mensuration etc.

To understand more about the geometric features and properties of cubes, formulas related to mensuration and the principles of cubical or octahedral symmetry - you might find it useful to read the properties of a Cube tutorial over here. Many of these concepts are a part of the Grade 9 and 10 Mathematics syllabus of the UK GCSE curriculum, Common Core Standards in the US, ICSE/CBSE/SSC syllabus in India. You may check out our free and printable worksheets for Common Core and GCSE.