Subwoofer Box Volume Calculator
Work out the net internal volume of a speaker or subwoofer enclosure from its internal dimensions, then subtract the driver, port and bracing displacements. Net volume is the figure that matters when matching a box to a driver's recommended alignment.
Enter Values
How to use this calculator
- Measure the inside length, width and height of the box in millimetres (subtract the panel thickness from the outside measurements).
- Enter the driver's displacement in litres from its data sheet, if known.
- Enter the combined port and internal-bracing displacement in litres, then read the net internal volume.
How it works
Gross internal volume in litres = internal length × width × height (in mm) ÷ 1,000,000. Net volume = gross − driver displacement − port and bracing displacement. The cubic-feet figure divides litres by 28.3168.
Worked example
Worked example. A box measuring 400 × 300 × 350 mm internally has a gross volume of 42,000,000 ÷ 1,000,000 = 42 L. With a 2 L driver and 0.5 L of bracing, net volume = 42 − 2 − 0.5 = 39.5 L (1.395 ft³).
Common mistakes
- Using the outside dimensions instead of the internal dimensions, which overstates the volume.
- Forgetting to subtract the driver, port and bracing displacements from the gross figure.
- Mixing units — all three dimensions must be in millimetres for the formula to work.
Frequently asked questions
Should I use gross or net volume when choosing a box?
Use net volume. Driver alignment tables and modelling software refer to the air volume the driver actually sees, which is the gross volume minus everything that takes up space inside.
Where do I find the driver displacement?
The driver's data sheet usually lists it directly (often as Vd or displaced volume). If not, you can estimate it from the cone and magnet dimensions, but the published figure is best.
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Cite this tool
Zerdly. (2026). Subwoofer Box Volume Calculator. Retrieved from https://www.zerdly.com/tools/subwoofer-box-volume-calculator/
Tip: Enter any known values to calculate the remaining results.
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