Speaker Box Calculator – Enclosure Volume & Board Cutting Guide

Speaker Box Calculator

This speaker box calculator (or subwoofer box calculator) helps you determine the board measurements to cut when building a speaker enclosure of your own. It also works as a speaker box volume calculator: it finds the internal volume of your box from its outer dimensions, board thickness, speaker driver displacement, and tube port (if needed). As a bonus, we've included a speaker driver displacement calculator for your convenience. 🔊

In the article below, you'll learn some guidelines on how to build a speaker box and how to calculate speaker box volume yourself — and don't miss the sample calculation for a 12-inch speaker box at the end.

Building a speaker box

Building your very own speaker or loudspeaker — whether it's a full-range speaker, a woofer, a mid-range speaker, or a tweeter — is a fun experience. It challenges our creativity in woodworking, electronics, and our understanding of sound.

Building a speaker box means having full control over its design and size — not just over the speaker driver you want to use, but also over the sound quality. In this basic guide, we focus on the speaker box itself, the volume displaced by the speaker driver, and the speaker tube port (if you need one).

How to build a speaker box?

Building a speaker box is like building any kind of wooden box, except that it has no moving parts like lids or covers. We cut boards of wood or fiberboard to size and assemble them into a closed box with proper sealing, using enough glue or caulking on the joints.

The first step is to decide on the design and size. If you're keen on clean audio and deep bass, your best choice is a ported speaker box. If bass is not your main concern, a sealed speaker box should be your go-to option.

Once you've decided, the next step is to determine the board panels' measurements. Each panel's dimensions depend on the box's outer dimensions and the board's thickness. For example, if the top and bottom panels overlap everything, the front panel's height is smaller than the box's height by twice the board's thickness — and the same logic applies to every inset panel. Our calculator offers six assembly cases to choose from, so you can decide which faces overlap and which are inset.

After cutting your boards, it's a matter of assembling the panels. You can butt-joint the pieces together or miter them for a seamless look — butt joints are stronger, easier to make, easier to seal, and still aesthetically pleasing.

How to use our speaker box calculator?

1. Choose your unit system — American (inches) or metric (centimeters).
2. Choose the assembly case. At first glance the cases look identical, but during assembly you might want to recess a face or two for added character: cases 1–2 recess the front and back, cases 3–4 recess the side panels, cases 5–6 recess the top and bottom. The internal volume is the same either way — only the cutting guide changes.
3. Enter your speaker box's outside dimensions: width, height, and depth.
4. Input the board thickness. Speaker boxes are typically made of 3/4-inch to 1-inch (20 mm to 25 mm) thick boards. The board cutting guide appears with your results.
5. If you're building a ported speaker box, select Yes in the ported field to reveal the port diameter, port length, and port count fields. The port's displaced volume is subtracted from the box's internal volume — this feature also makes the tool a subwoofer box calculator.
6. If you already have a speaker driver, select Yes in the driver field and input the cone diameter, mounting depth, magnet diameter, and magnet depth. The driver's displacement is estimated and subtracted from the internal volume automatically.

How to calculate speaker box volume?

To estimate the speaker box volume, determine the box's internal dimensions and multiply them together. Since the board thickness t is uniform throughout the box, each internal dimension is the outer dimension minus twice the thickness:

The port volume is the volume of a cylinder (multiplied by the number of ports):

The speaker driver displacement is approximated as a cone (the diaphragm and basket) plus a cylinder (the magnet):

Sample calculation of speaker box volume

Let's design a box for a 12-inch subwoofer using 3/4-inch (0.75 in) fiberboard, with outer dimensions of 14 × 18 × 12 inches (W × H × D):

• Internal dimensions: (14 − 1.5) × (18 − 1.5) × (12 − 1.5) = 12.5 × 16.5 × 10.5 in
• Gross internal volume: 12.5 × 16.5 × 10.5 = 2165.6 in³ ≈ 1.253 ft³ ≈ 35.5 L — a classic sealed-box volume for a 12-inch driver.
• Add a 4-inch diameter, 6-inch long port: V_port = π × 2² × 6 ≈ 75.4 in³, leaving about 2090.2 in³ (1.21 ft³).
• Subtract the driver displacement (12-inch cone, 5.5 in mounting depth, 6-inch magnet 1.5 in deep): V_driver ≈ ⅓π × 6² × 4 + π × 3² × 1.5 ≈ 193.2 in³ ≈ 3.2 L.
• Net internal volume: 2165.6 − 75.4 − 193.2 ≈ 1897 in³ ≈ 1.10 ft³ ≈ 31.1 L.

With assembly case 1 (top and bottom overlap everything), the cutting guide reads: front/back 12.5 × 16.5 in, sides 12 × 16.5 in, top/bottom 14 × 12 in — two pieces of each.

Frequently Asked Questions

Sealed or ported speaker box — which should I build?

A sealed box is smaller, easier to build, and gives tight, accurate bass. A ported box is larger and slightly harder to tune, but it plays louder and digs deeper in the low frequencies. For a first build, a sealed box is the safer choice.

Does the assembly case change the internal volume?

No. All six assembly cases produce exactly the same internal volume — the outer dimensions and wall thickness are identical. The cases only change which panels span the full outer dimensions and which are inset, i.e., the sizes of the boards you cut.

How thick should the boards be?

Use 3/4-inch (about 19–20 mm) MDF or plywood for most speaker boxes, and up to 1 inch (25 mm) for large or high-power subwoofers. Thicker walls reduce panel resonance and unwanted vibration.

Why subtract the port and driver volumes?

The speaker's acoustic behavior depends on the air volume inside the enclosure. Anything that occupies internal space — the port tube, the driver's magnet and cone assembly, or internal bracing — reduces that air volume, so it must be subtracted to get the net volume the driver actually "sees".