Sealed Subwoofer Boxes

Use a flexible tape measure and reach through the empty speaker mounting hole to measure.  You want three measurements:  length, depth and height.  Do this for each chamber.

L x W (or D) x H = cubic inches.  There are 1728 cubic inches per cubic foot ( remember this number by multiplying 12 X 12 X 12 ).  So you will divide 1728 into the total cubic inches you arrived at.

example:  You measure 9.5 X 14 X 13.25 on the inside of the box.  Multiplied, the cubic inches is 1762.  1762 / 1728 = 1.02 cubic feet.

And yes, both chambers should be equal or very nearly so.

Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.