It is called a foot, because it was originally based on the length of a foot.
Inch is derived from the old English ince, which in turn came from the Latin unit uncia, which was one-twelfth of a Roman foot.
Formula to convert feet to inches.
The relationship between a foot and an inch is that, 1 foot is equal to 12 inches.
Therefore, if you want to convert ft to in, you multiply the feet by 12.
Length in In = Length in ft x 12
Convert 10ft to In.
= 10 x 12
= 120 Inches