Speaker Box Calculator

Work out a speaker enclosure's net internal airspace from its external dimensions and panel thickness, minus the volume displaced by the driver and bracing.

Quick Facts

Formula
Net volume = (L−2t)(W−2t)(H−2t) − displacement
t is panel thickness; each internal dimension loses 2t because wood sits on both sides of the box.
Unit conversion
1,728 in³ = 1 ft³
1 in³ ≈ 0.0163871 liters; 1 ft³ ≈ 28.317 liters.

Your Results

Calculated
Net internal volume
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Usable airspace in cubic feet
Net internal volume (L)
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Same airspace in liters
Gross internal volume
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Before displacement, in cubic feet
Displacement removed
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Driver + bracing volume taken out

Ready

Enter your box dimensions, panel thickness, and driver displacement, then press Calculate.

How speaker box volume is calculated

Speaker enclosure builders design a box around a target net internal air volume — the space the driver actually "sees" once panels, bracing, and the driver itself are accounted for. This calculator uses the standard geometry approach: start from the box's outside dimensions, subtract the wood panels to get the inside dimensions, multiply those together for the gross internal volume, then subtract whatever space the driver and bracing take up to arrive at the net usable airspace.

The formula

For a rectangular box with external width W, height H, and depth D, built from panels of thickness t:

  • Internal width = W − 2t, internal height = H − 2t, internal depth = D − 2t (thickness is removed from both sides of each dimension).
  • Gross internal volume = internal width × internal height × internal depth, in cubic inches.
  • Net internal volume = gross internal volume − (driver and bracing displacement × number of drivers).

Cubic inches convert to cubic feet by dividing by 1,728 (12³), and to liters by multiplying by 0.0163871. Net volume, not gross volume, is what should be compared against a driver's recommended sealed or ported enclosure volume, since the manufacturer's spec already assumes real driver and bracing displacement is excluded.

Getting good inputs

  • Measure external dimensions with the panels already in the orientation you plan to build, since width/height/depth are not interchangeable for non-cube boxes.
  • Use the actual panel thickness you'll build with (0.75 in / 3/4 in MDF is the most common car-audio and home-subwoofer choice).
  • Displacement should include the driver's magnet and basket below the mounting flange, plus any internal bracing, port tubing, or bulky wiring — a mid-size 10–12 in woofer with modest bracing is commonly estimated around 40–90 in³.

Frequently Asked Questions

How do you calculate speaker box internal volume?
Measure the box's external width, height, and depth, then subtract twice the panel thickness from each dimension to get the internal (inside-the-wood) width, height, and depth, since the panel material takes up space on both sides of the box. Multiply those three internal dimensions together for the gross internal volume in cubic inches, then subtract the space taken up by the driver's magnet and basket plus any internal bracing to get the net usable airspace.
Why subtract driver and bracing displacement?
A speaker driver's magnet structure and basket, along with any internal bracing, ports, or wiring, occupy real space inside the box that is not available as usable air volume. Sealed and ported box designs are tuned to a specific net air volume, so ignoring displacement makes the actual box larger (acoustically) than the design calls for, changing the intended low-frequency response.
How do I convert cubic inches to cubic feet or liters?
There are 1,728 cubic inches in a cubic foot (12 x 12 x 12), so divide cubic inches by 1,728 to get cubic feet. To convert to liters, multiply cubic inches by 0.0163871 (since 1 cubic inch equals about 16.387 cubic centimeters, or 0.0163871 liters).
Does this include port volume for a ported (vented) box?
No. This calculator computes the net internal airspace of the enclosure itself from its dimensions and displacement. For a ported design, the port's own internal volume also displaces air and should be included in the displacement figure if you want the net airspace around the port, since the port tube's tuned length and diameter are calculated separately from box volume.

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