[Aegis]

The code says a square 4x1 1/2 box is 21in3.

How is this number figured out?
I would think its 4x4x1 1/2 but that comes up to 24.

I know I'm missing something but I can't figure out what. Thoughts?

 

[Dennis Alwon]

I think the numbers in the NEC are the inside dimensions so it is not quite what you think it is.

 

[Aegis]

I think the numbers in the NEC are the inside dimensions so it is not quite what you think it is.

Got it, makes sense.

 

[FrunkSlammer]

Yeah box dimensions, outside.. box fill dimensions, inside.

 

[HARRY304E]

Got it, makes sense.

Also they may be rounding down for a whole number.