Measure the length of a wall in a room. For example, assume a wall measures 8 feet.
Measure the length of the opposite wall in the same room. For example, assume the opposite wall also measures 8 feet.
Measure the remaining walls in the room. For example, assume the two remaining walls both measure 12 feet.
Add the length measurement of all of the room's walls. Continuing the same example, 8 + 8 + 12 + 12 = 40 linear feet. This figure represents the linear footage of the room.