You don't. Its cubinc footage, not square footage.
In order to get the square footage you need to take 13' times 15' and you will get the square footage
1200
Multiplying length by width equals square footage
The square footage of a baseball field is 4,569ft2
The square footage of a lot measuring 81x180x113x180 is 20,340 square feet. Square footage is found by multiplying the length by the width of an area.
The square footage would be 25 times 12 or 300 square feet.
Read your own question! The square footage is 20!
Square footage is a measure of an area. It is usually for areas for which square feet is a sensible measurement unit, such as a room, or a house. However, we have had people asking about the square footage of countries!
Length x width = square footage
how is bi-level square footage calculated
what is the square footage