Subwoofer Box Calculator

Gross volume, displacement and net airspace

For a rectangular enclosure entered by its outside dimensions, the calculator first removes two panel thicknesses from each axis:

internal width = external width − (2 × panel thickness)

gross internal volume = internal width × internal height × internal depth

Net airspace is what remains after everything inside the enclosure has been accounted for:

net volume = gross volume − driver displacement − bracing − terminal/other − port displacement

Driver displacement is the number of drivers multiplied by the displacement of one driver. Use the figure in the exact driver’s specification sheet; basket and motor shapes vary too much for cone diameter alone to provide a reliable value. Rockford Fosgate’s enclosure guide likewise treats speaker displacement as volume that must be removed from available airspace.

When solve one dimension is selected, the calculation runs in reverse. It adds the entered displacements to the manufacturer’s target net volume, divides that required gross volume by the other two internal dimensions, then adds two panel thicknesses to report the missing outside dimension. The answer assumes a plain rectangular box with uniform panels.

Worked example

Consider an outside box measuring 24 × 14 × 16 in, built from 0.75 in panels. Its internal dimensions are 22.5 × 12.5 × 14.5 in, giving about 4,078.1 in³ or 2.360 ft³ gross. If one driver occupies 0.10 ft³, the bracing 0.04 ft³ and the terminal 0.01 ft³, the net volume is about 2.210 ft³ before any port deduction.

For an irregular enclosure, calculate or measure its gross internal volume with suitable geometry or CAD, then use manual gross mode to apply the same deductions. Panel thickness and external dimensions do not participate in that mode.

Ported boxes: volume is not tuning

For a ported enclosure, this tool can subtract a directly entered port displacement or the occupied geometric volume of a round or rectangular port from the box. Use the port’s physical outside or occupied dimensions consistently. KICKER’s box-building guidance says a port’s displacement must be added to the gross design volume, and its manuals demonstrate using the port’s outside dimensions.

That subtraction does not choose port area, calculate port length, set tuning frequency or check air velocity. Port design depends on the driver, target alignment and the final net enclosure volume. Follow the enclosure drawing or port specification supplied by the driver manufacturer, or use a specialist design tool. The sealed/ported choice here controls which displacement inputs apply; it is not an acoustic recommendation.

Before cutting panels

Confirm whether the manufacturer’s stated volume already includes driver or port displacement—published conventions differ. Match the exact model and enclosure type, keep every input in the selected unit system, and check that internal dimensions remain positive. This calculator does not create a cut list, account for rebates, double baffles, angled panels or shared port walls, or assess bracing and structural suitability.

Cutting sheet material creates dust, noise and kickback hazards. Follow the tool and material manufacturers’ instructions, use effective dust collection and suitable eye, respiratory and hearing protection, and keep guards in place. OSHA’s woodworking guidance covers machine and wood-dust hazards. During system testing, control playback level and duration; NIOSH identifies repeated occupational exposure at 85 dBA or above as a hearing risk.

Sources: MTX enclosure construction and volume formulas, KICKER box-building guidance, Rockford Fosgate enclosure guide, OSHA woodworking hazards and solutions, and CDC/NIOSH noise guidance. Sources and product scope reviewed 16 July 2026.