What is cubic feet of a 10'x10'X8'?

Answer 1

Any length you want (greater than zero).

Or to put it another way:

• cubic feet are a measure of volume; whereas
• how long something is is a measure of length

they measure different things.

If you have a 10 cu ft box, 1 ft by 2 ft by 5 ft which side represents how long it is?

Alternatively, the 10 cu ft box could be 4 in (1/3 ft) x 10 ft by 3 ft; now how long is it?

Answer 2

10' * 10' * 10' = 1000 cubic feet.