Sub Box Calculator › Subwoofer box volume calculator
Subwoofer box volume calculator
Enter the outside dimensions and the wood thickness. You get the inside dimensions and the box volume in cubic feet and liters — gross and net, after the sub, the port and the bracing are subtracted.
How box volume is calculated
Subtract the walls from each outside dimension and multiply what is left:
Example: a box 30 × 15 × 16″ outside from ¾″ MDF is 28.5 × 13.5 × 14.5″ inside, which is 5,579 in³ or 3.23 ft³ gross (91.4 L).
Gross vs net volume
The sub only “feels” the air in the box. The sub’s own motor and basket, a port, a slot wall and braces take part of the space. What is left is the net volume, and that is the number the manufacturer’s recommendation and the box design mean. A 12″ sub displaces about 0.05–0.15 ft³ depending on the magnet; a slot port in a 2.5 ft³ box can take 0.5–0.8 ft³. More in net vs gross volume.
Wedge boxes
Boxes behind a truck seat or in a sloped trunk are often wedges: deeper at the bottom than at the top. The side view is a trapezoid, so the calculator uses the average of the inside depths at the top and at the bottom. That is accurate to a few percent; the full calculator draws the angled panel exactly.
Design the whole box→FAQ
How do I calculate cubic feet of a sub box?
Measure the inside width, height and depth in inches, multiply them and divide by 1,728. With outside dimensions, first subtract two wood thicknesses from each one.
Does the subwoofer take up box volume?
Yes. The motor and basket inside the box displace air — usually 0.05–0.15 ft³ for a 12″ sub. The manufacturer lists it as displacement; subtract it, and the port, to get the net volume.
How many liters is a cubic foot?
One cubic foot is 28.32 liters; one liter is 0.0353 ft³.