Minecraft surface area calculator

Usually you can calculate the surface area of a rectangular prism with side a, b and c using the formula 2ab+2bc+2ac: http://www.math.com/tables/geometry/surfareas.htm#rec

However, in minecraft blocks can be part of two or three sides (in the case of a corner), which means that you need fewer blocks to cover the surface of such a prism than the result this formula. The formula is: (L*W*H)-((L-2)*(W-2)*(H-2)).
You can derive this by taking the volume of the block then subtracting the inner volume from the main volume. Though beware that this does not work with sides of 1 or 2, in those cases it's just L*W*H.

Length:
Width:
Height:

In Excel, the formula, with the length, width, and height in A1, A2, and A3 respectively, is:
=(A1*A2*A3)-((A1-2)*(A2-2)*(A3-2))
Note: does not work with sides of 1 or 2, in that case it's just =A1*A2*A3.

Source code: https://github.com/vzx/minecraft-surface-area-calculator