Net volume of your sub box, or the width you need for a target ft³: sub and port displacement, double baffle, wedge boxes and a cut sheet in fractions.
Box type
Sealed
Ported
Sealed
Ported
Sealed
Ported
I know
The
outside
size
volume
I
want
The outside size
The volume I want
The outside size
The volume I want
Outside width (in)
Outside height (in)
Outside depth (in)
Wood thickness
= 19 mm
Number of subs
1
2
3
4
1
2
3
4
Net volume (air for the sub)
2.98 ft³ (84.3 L)
Gross inside volume
2.98 ft³ (84.3 L)
Inside size (W × H × avg D)
30 1/2" × 13 1/2" × 12 1/2"
3D preview
Drag sideways to turn it. Tap to show or hide the sizes.
Sub circles are a sketch. Cut the hole your sub’s manual gives.
Cut sheet
Outside sizes, 3/4" wood. Cut one piece, check it, then cut the rest.
Cut sheet
Piece
Qty
Size
Front (baffle)
1
32" × 15"
Back
1
32" × 15"
Top and bottom
2
32" × 12 1/2"
Sides
2
13 1/2" × 12 1/2"
Board area: 14.6 sq ft, about 0.46 of a 4 × 8 sheet
Starting points, not guarantees. Your sub’s manual wins: check its recommended box and tuning.
How it works
Pick sealed or ported, then either type the outside size of a box you have in mind, or the net volume your sub wants and the height and depth of your space. Add the wood thickness, how many subs and the displacement from the sub’s manual. Ported: type the port’s volume, or its type, size and length (round, aero or slot) and the app works out how much box it takes up, the tuning in Hz it gives, and draws it in the 3D preview. You get the net volume, the gross volume, the inside size and a cut sheet in fractions of an inch.
Example: a 30 × 15 × 16 in box in 3/4" MDF is 28.5 × 13.5 × 14.5 in inside, 5,578.9 in³ or 3.23 ft³ gross. Two subs at 0.15 ft³ each, a 0.5 ft³ port and 0.05 ft³ of bracing take 0.85 ft³, which leaves 2.38 ft³ net.
Working backward: for 2 ft³ net with one sub (0.1 ft³) in a space 15 in tall and 16 in deep, the box must be 20 1/16 in wide. If you only have 18 in, the most that fits is 1.77 ft³ net.
Frequently asked questions
What is the difference between gross and net volume?
Gross is all the air inside the walls. Net is what the sub actually works with: gross minus the sub’s own displacement, the port and any bracing. Sub manuals give net volume.
Does a double baffle change the volume?
Yes. The second layer sits inside the box, so the inside depth gets one more wood thickness shorter. With 3/4" MDF on a 28.5 × 13.5 in inside face that is 288.6 in³, about 0.17 ft³.
How do I work out a wedge box for a truck?
Measure the depth at the floor and at the top of the space. A 36 × 14 in wedge that is 16 in deep at the bottom and 10 in at the top holds 2.85 ft³ gross in 3/4" MDF, with the back leaning 23.2° from vertical.
Is MDF or plywood better?
Both work. 3/4" MDF is dense, flat and cheap; birch plywood is lighter and stronger at the screws. What matters most is glue on every joint and an airtight seal.
How much box does the port take up?
Its inside area times its length, times the number of ports. Two 4 in round ports 12 in long take up 2 × 12.57 × 12 = 301.6 in³, about 0.17 ft³. A slot also counts the board that forms it: a 3 × 13.5 in slot 30 in long in 3/4" MDF takes up (40.5 + 10.125) × 30 = 1,518.8 in³, about 0.88 ft³. Pick Round, Aero or Slot under Port and the calculator takes it off the net volume for you.
What will my ported box tune to?
Describe the port by its size and the result shows the tuning, worked out from the net volume with the Port tool’s formula. A 30 × 15 × 16 in box in 3/4" MDF with one sub (0.1 ft³) and two 4 in round ports 12 in long has 5,104 in³ net (2.95 ft³): Fb = √(1.463 × 10⁷ × 2 × 2² ÷ (5,104 × (12 + 2.93))) = 39.2 Hz. It is an estimate: your sub’s manual and real-world tuning can differ by a few hertz, so build the port a little long and trim.