On just paper you can figure out how much volume your brace will take up if it was a solid piece. Then figure out the volume of the pieces you will cut out of the solid brace. Subtract that volume and there is your net volume of your brace.

Calculator works the same if you know the dimensions of your cutouts only and not the volumes of each piece. I tend to do waffle style so the calculator is not useful to me. But when doing window style bracing it is very useful.

 

So maybe something like, 2*2*18/1728=0.04166666666 * 2 braces = 08333333333 in^3?

 

Not sure what your numbers represent.

 

2x2 pieces of wood.

 

Are you doing window frame bracing or dowel rod style bracing?

 

There is a brace volume calculator Here